1586 in the work shop

this is the pic of the 1586 I picked up this summer got it at auction for 2800.00 wasn't looking for one but wasn't going to let her be parted out. it was sold saying it was running in the field and the farmer heard a loud pop and stopped moving. and now looking what it needs to fix. has a good reman motor in it but has fuel leak from return line form what it looks like. took top link cover off and the ring and pinion are turning but neither tire moves so I saying right now final drive and it is planetary drive set up. looks like some grinded metal shaving on edge of case in back. the shifter will go in all 3 gears, pto works and can get shifter to go in reverse but will not go in park. what do you guys think do I have 2 different problems? or is it the same problem with final drive. or am I missing something? also going to switch the pto from 1000 to a 5401000 pto and drain the back out and wash with solvent to get it good and clean.
anybody that's dealt with this feel free to comment as never been in the rear end of this size tractor. also plan on paint job and getting bugs out a electric system, cab kit and ac working.
thanks guys

I'm not for sure how this will work, but maybe put it in gear like you are driving it, let the clutch out, and then apply one brake at a time. I would think that it isn't moving because if something in the final drive broke, that side has no load so is spinning continuously. I just wonder if a brake was applied to that side if it would stop it from freewheeling and make then side that isn't broke try to move the tractor. Unless it is broken before the brake. Not sure how the planetary set up on a 15 works, but I would assume the brake and bull pinion set up is similar to the smaller models. If it had a broken bull pinion, that wouldn't be too bad a deal to fix, just pull axle and brake housing. Also not sure if they are the same as the smaller models in that being you can drain the oil on one side or the other to see which side has more metal in it, pointing to the side you need to look at.

Applying the brake would work if the problem is in the planetary itself, but most likely the problem is in the drop gear from differential to planetary drive gear or in the differential itself. We had some failures due to the ball bearings on that drop gear failing and chewing up lots of parts. We informed most all customers in our area that we could install a flat bower roller bearing in two locations on each side that originally had ball bearings and reduce problems considerably. Did that to several.

But, draining each section will pinpoint problem area were ever it is.

Differential went out of the tractor