i had a 1983 843 and it had geroler motors , they are re-buildable , the key is CLEAN workplace. the bad news is ...if it's not a problem with your chains and sprockets,you most likely need more than just a motor rebuild . the pump /motor hydro circuit is semi closed ..the same fluid moves back and forth as you drive forwards and backwards only a small amount is exchanged to the reservoir thru the case drain line on the motor. if you have significant damage to your motor the ground up metal parts have gone to your rotating group in the pump...the pump is very sensitive to contamination . i had a drive problem, i put the machine on the trailer, 300 ft. and then unloaded it at the shop another 50 ft. when i broke it down the rotating group was destroyed, the little pistons were flopping around in over-sized holes. with the hrs on my machine i opted for rebuilt motors and pump unit complete ..total cost about 5000$us. that's not a dealer price ...haha i called around to hydraulic suppliers ...as soon as i gave him my part numbers he said ..oh you have a 843 bobcat we have the complete set up for you ,,and so he did....