I would start by de-greasing / pressure washing the entire vehicle inside and out to get an idea of what is going on in the tub. Next I would spray all the sprocket tubes and bolts on the axles with Pb blaster over and over for a few days as more than likely the axles will need to come out. You need to do this in preparation to replace the axle bearings search for buffalo bearing on the board. in the mean time search the board there is a thread about proper belt size for the Hustler. Make sure the chains are in good shape and lubed if not replace them.
T-20 drain it and pay attention to what type of fluid comes out. Reddish ATF or type F good. Gear oil BAD. again do a search on the T-20 about fluid but basically one tube of limited slip stuff and fill with type F until it runs out the Bottom hole.
That should get you started for about a week or so. Anything specific you find post it up and people are more than willing to help. Pictures work the best so upload some if you can.
Welcome to the board
Mike
"Don't worry my Dad's a TV repairman, he has an excellent set of tools..I can fix It"