When the thread started I was certain it would end up here, If it were mine I would get a flat thick piece of glass, some 400 grit wet emery cloth and using light oil I would first polish the brass piston cups, then figure 8 the piston block commutator area , if you watch carefully you can see when the wear areas come out, I turn the block every few turns to try to keep it as square as possible, if the brass plates were not so badly worn I would also renew them in the same fashion but as was stated they are pretty rough. I have done many of these and other hydrostat pumps in this manner with great success. An educated guess is that at some point in time drive hoses were changed with no regard to keeping the hoses and fittings spotlessly clean. I did this work in a professional shop where I worked for 50+ years and sent them out the door guaranteed. Looking back I see this is an old thread but my advice still stands for those who will be reading in the future.
