Pin fell back inside the central shaft.

I would expect that to come as part of the shaft so don't expect to buy another one without the shaft. Factory pressed in supposed to never come out.

I an sorry but the only Rod in the back of a K45SS is the pivot hinge pin that holds the motor head onto the base. if it fell out then the answer is simple. Turn the mixer upside down and wiggle the base while sliding the pin back in. Once the pin is back in place, there is a set screw in the middle of the shaft that you can see while you are replacing the pin, turn this back down with a flat head screwdriver untill it is firmly against the hinge pin. The culprit of the problem is this set screw. It came loose and allowed your hinge pin to vibrate out and then fall down or fall out as you said. once the set screw is back in place you will be fine. To avoid this problem in the future you might remove the screw entirely and put a drop of "Lock-Tight" on it that will help hold the setscrew in place for a very long time.

If it is model 5KPM5 then there is a pin through the shaft inside the planetary that engages the pinion gear. There is a circlip above the gear clipped to the shaft that holds the gear into engagement with the pin. I've not seen one drop the shaft out in my life, the circlip would need to pop off & the gear would need to jump up and then the pin would need to slide out. All the bits would be there inside the planetary waiting for you to discover them.

The cross feed drive shaft is connected to the cross feed spindle via a coupling that resembles a universal joint that is threaded onto the end of the cross feed spindle. Either one of the roll pin holes in the drive shaft coupling has worn and the roll pin fell out or it has broken, or the coupling could have came un-screwed from the cross feed spindle. Remove the 4 bolts that hold the cross feed gearbox on and slowly pull it away from the machine and you should see the coupling I'm describing. My guess is that the roll pin broke or fell out due to wear. You can buy a new drive shaft and coupling or drill and install the next larger roll pin. Either way you should download a parts list for your machine. Just search for it, they can be downloaded free.

The rear axle shaft?? Or the entire axle? I'm going to go with the axle shaft. Secure the vehicle. Loosen the lug nuts. Jack it up. Take the wheel and tire off. Remove the caliper and/or bracket. Remove the rotor. Place a pan under the rear differential cover. Remove the rear differential cover. Spin the axle shaft to reveal the center pin. Locate the 8mm-5/16 bolt that holds the center pin in place. Remove that bolt. Slide the center pin out, BUT DON'T TURN THE AXLE SHAFTS WHILE ITS OUT! Push the axle shaft in from the outer portion (where the wheel goes). A "C" clip will fall out inside of the differential. Pull the axle shaft out. Slide the center pin back in. Replace the 8mm-5/16 locking bolt and spin it a few times to keep everything in place.

the pin was used for shipping it is no longer needed.cannot think what you could of done but possible the triangular skate plate became crooked

Yes, and yes. A small hook is needed, a small crochet hook will work. The latch is on the side farthest away from the center of the camera. You are pulling up to free the door latch. The rewind knob is tricky, but possible. Keep the door open while re-assembling as the center shaft will be loose till you get the knob on. The handle and pin are easy, assemble them 1st. Hold the center shaft, put the coil spring in, then the washer and finally the spring plate. Guide the handle/knob assembly onto the shaft with the parts. It is tricky to hold it all in place, but is possible.

Hi,
that small pin is for support and not to bend front cover towards lens mechanism.
Small pin will be installed in center of lens assembly with head upward.
Let me know if you need further info.

It should have a bolt through a pin holding it in place inside the diff cover. Remove the cover, find the small bolt going through the pin, remove the bolt and pin, and push inward on the axle from the hub. The retainer clip should fall, allowing you to pull the axle shaft out.
Good luck!