When turn off. makes a humming sound. compressor seems to be running.

Many of these consumer units use low grade copper for their refrigeration connections. The oil is a sure fire indicator of your seemingly correct diagnosis. Unless you have the proper refrigeration tools to repair and recharge the unit it may not be cost effective to try for a repair, as if this is the issue another leak is likely to occur. Many of these units come with 5 year compressor warranties though, so a quick check to make sure the leak is in the refrigerant piping and not on the compressor itself may be worthwhile. If your warranty has not run out it could be beneficial to find the exact source of the leak.

Change the fan capacitor.

check to make sure the compressor is running. try smacking it 5/6 times with a hammer while it's running, surrounding lights should dim for a second, should have low hum sound. This solved my problem

It is probably the start device(the coil looking things), as long as you don't hear the compressor humming. A loud hum is a lock compressor and the cost would be far greater than a new unit.

The black cylinder is the compressor. It sounds like your unit is cycling the compressor for some reason. If the compressor starts, runs fine, and removes water when you set the humidity control to the driest setting the compressor is probably OK and the problem may be with the humidity control causing the dehumidifier to "short cycle" for some reason. You may need to change the humidity control or relocate the dehumidifier in your crawl space.
If the compressor attempts to start, and then sits quiet for 10 minutes, and then attempts to start again, you have a problem with the dehumidifier. There are a few things that can cause this problem:
Low refrigerant charge
Bad compressor capacitor
Bad compressor overload
Plugged capillary tube or broken expansion valve
are the common causes of this behavior. If you suspect one of these problems, call the factory service department at 1-800-533-7533 for help.

Good luck with your dehumidiifer.

sounds like the compressor is seized.

remove the back airfilter, and touch the tubes while the unit is running, if nice and cold, all is well, there just isnt any moisture there. but if compressor is running and tubes are warm , means freon/coolant has leaked out

Could be a failed compressor start relay. They are replaceable. Get one at an appliance parts store for your model or a generic one. Make sure you are unplugged before changing.

Your unit is probably operating in defrost mode. When you use a dehumidifier in a cold room, the condensing coils can freeze water. The unit senses this and thus stops the compressor until the water frozen on the coils melts. Then it resumes its cycle. This is a problem you will have during the winter months. It makes the operation of the unit inefficient, but this is otherwise normal behavior.

Sounds like the unit needs re-gassing and checking for leaks. It is not unusual for a 3-year old unit to require this - especially dehumidifiers as they are often not used all year round, and the seals that stop the gas from leaking are prone to settling and drying out when not in use. This is not a procedure that you are permitted to carry out yourself, just call a local HVAC/Fridge repairer and see what they quote - the job itself is simple enough depending on the leaks and if anything needs replacing, but the gas itself is getting costly. Make sure they do a leak test first. If not topped up with gas then don't run the compressor - the lubricant that protects the compressor is mixed in with the refrigerant gas and will dry out quickly if the gas has leaked. Hope this helps - please ask for more info if you need it :)