Dresser 1991 TD-8 transmission questions

I stopped to look at a TD-8 G dozer sitting besides the road. They want $8500 and said the 3rd gear slips but one & two were good. Said the screen hydraulic supply was plugged. They had done quite a bit of work to repair the engine, new pistons, rod bearings, replaced some lifting rods etc. The engine started easily and idled well. The tracks are worn, the roller pins had been turned at least once but the sprockets still had life.
How much would it cost to repair the transmission? Any comments or recommendations?

Dresser 1991 TD-8 transmission questions