I don't know much about JD, how well do they hold up and what are major problems with them? What other dozers use the hystat? And is it similar to the drive system for excavators?
I think that is a Leibherr built machine, just branded Deere. Different machine from the smaller units. Check with your local dealer if they have any experience repairing the machines. Local dealer here suggested a friend not buy one. Parts availability may be slim, slow, and expensive even by Deere standards.
950/1050J's are still leib-deere, K series are deere-built machines.