I have a gl2 that fell off the tripod. now i can't use any of the aperture settings, including color gain. it seems that part of the lens unit is coming out of the housing slightly, and i can see a bit of one of the gears inside.

That's because you are using Auto mode, aperture and shutter speed is done automatically by the camera. Try to use the manual mode, ISO 800, speed 60 and lens aperture 2.8. Use a tripod to avoid image blur due to camera shake

Set the exposure mode to "M" (Manual). You'll have to set both the aperture and shutter speed yourself.

You'll also get no exposure assistance from the camera's light meter. You can review the picture after taking one and/or use the histogram to tune the exposure.

You did not provide enough information to determine what your problem is. For example, were the pictures all light or all dark. Knowing this lens, I will assume that they were all dark. So...

1) This is a very, very slow manual-focus lens. It will not auto focus. It must be manually focused very precisely because it has virtually no depth of field.
2) Depending on your camera, your internal light meter may not work. On my camera (Nikon D-90), it does. If it does not on yours and I suspect that may be your problem, you're going to have to shoot everything manually, i.e. setting the shutter speed and lens opening yourself. You can use your internal light meter to help you get started by taking your light reading before you install the lens...preferably using the aperture only setting where you set the aperture at f8 which I think is the speed of the Opteka and let the camera set the shutter speed. Make a note of the shutter speed then attach the Opteka to the camera and mount the lens on a tripod with the camera attached.
Then set your camera mode to manual and set the aperture to match the lens (f8, I think). Set the shutter speed at the speed you noted earlier. Shoot a picture using a remote shutter release or the self timer. This lens is so slow that unless you're in exceptionally bright conditions you will get fuzzy pictures due to camera movement at full zoom of 1200m and above if you're using the 2X doubler. I would start shooting at minimum zoom of 650 without the 2X doubler. Shoot a picture. and check the result.

You should have an image but it may be too light or too dark.

If its too light you'll need to increase the shutter speed or stop down the aperture to, say, f11...or both. Make the adjustment and shoot another picture. Remember that if you increase the aperture, you increase your depth of field, making focus less critical. If you increase the shutter speed you make camera or subject movement less critical.

If it's too dark, you can only increase the shutter speed because you can't open the lens any wider than f8. Make the adjustment and shoot the picture.

Keep doing this until the pictures are the way you want them.

This is a decent lens for the price and worth the little money they cost if you can't afford $10,000 plus for a high quality telephoto lens of this size. I would forget about the 2X doubler because as others have said, it further reduces the speed of an already very slow lens with such a high rate of magnification that a knat landing on the lens could cause the picture to blur from movement.

There is no communications between the camera and lens. When using a set up like this everything becomes manual and you must remember to stop down the aperture to your taking aperture before releasing the shutter. I don't know what camera or format you are going to use this lens with but assuming it is a digital "bridge" (a camera that is between an amateur and a pro) or a professional the sequence would be the same.
To view, focus and compose the lens would be set in this case F2, to select the correct light meter reading the lens is set (stopped) down to the taking aperture. The modes I've used for this have been mostly manual but lately I found that "AV" worked equally well and the camera metered to the proper exposure. Most times the camera was mounted on a tripod and the shutter was released with a electronic shutter release.
Sequence for taking a photo for me anyway was/is (with the camera mounted on a tripod) focus, compose, stop down to taking aperture, check metering and release the shutter if in AV mode or manual mode to set the shutter speed and release the shutter.
You will find that all makes of digital cameras will function differently so what sequence works for one won't work on others. This meaning I have had digital cameras that wouldn't meter through anything other then the lenses meant specifically for them.
Problems that I've had. Forgetting to stop down to taking aperture (like Duh), not fine focusing (manual), not trusting the in focus indicator, forgetting that the viewfinder is/was only 94% of the scene. Once a little time has been spent with a lens set up like this the rewards are far beyond the trivial annoyances. Have fun with it

I think the aperture is not shutting down to the opening you set it to. In an SLR, the aperture is normally fully open for viewing through the lens. When you press the button, the mirror flips up and the aperture closes to the figure you have set, then the shutter fires. If you have set a daytime aperture and the aperture sticks, you get a wide open aperture and an overexposed shot, but at night, you have set an open or almost open aperture anyway.

It is possible that the shutter is the problem, but the aperture is more likely to go wrong in my experience. It only takes a drop of oil on the blades. There ought to be a button or lever to shut the aperture down for depth of field preview which you could use to test this, or just look in the lens when the shutter fires to see if the aperture closes.

take the unit out into as bright a daylight as you can - the bottom line is you need light, hence flash or you need to take a longer exposure than you can hold - hence tripod - not having either of these means you need to get light into the speaker box You could try household lamps and point a few at the speaker cabinet - remember to set the white balance to tungsten also a camera lens with a good aperature F1.8 - Depth of field (focus) will not be very much at that aperture setting though

HI I AM SAGHA A CAMERA REPAIRER FROM MUMBAI,YOU SAID YOUR CAMERA WAS FALLEN ON THE FACE WITH LENS THEN STARTS OVR EXPOSING PICTURES THEN FIRST CHECK YOUR LENS'S APERTURE IS WORKING FINE OR NOT.ATTACH ANOTHER LENS TO YOUR CAMERA & THEN CHECK THE EXPOSURE THEN IT WILL BE CLEAR WHETHER YOUR CAMERA IS DEFECTIVE OR LENS IS DAMAGED INTERNALLY.REPLY ME ABOUT IT.THANK YOU & ALL THE BEST

The lens has a lever marked A/M near the aperture ring. If the lever is in the 'A' position, the lens will stay wide open until you trip the control lever at the back of the lens next to the rear optics. In the 'M' setting, you can see the aperture move as you change the f-stop setting on the ring. Set the lens to anything but wide open and move the control lever with your finger. You should see that aperture move.

Might Help:
Notes on G-type Nikkor and other CPU Nikkor lens
The G-type Nikkor lens has no aperture ring; aperture should be selected from camera body. Unlike other CPU Nikkor lenses, aperture does not need to be set to minimum (largest f-number). CPU Nikkor lenses other than G-type Nikkor lens have an aperture ring. Set the lens aperture to its minimum and lock. When the lens is not set to its minimum aperture setting and the power switch is turned on, "fEE" blinks in the control panel and viewfinder and the shutter cannot be released.

Make sure the aperture ring is set to the "A" position. If the lens doesn't have an auto aperture setting then I don't think the lens will work. There is a setting called "Using Aperture Ring" that you can setup using the menu and configuration that can be set to "Permitted" that will allow you to take pictures even if the aperture ring is not set on "A", but not sure how well this work for you, but should allow the shutter to work.