This is for a 1975 1650 with a S/N 540720. Last year I took time to fix oil leaks, the worst was the cork mounting gasket for the hydro. It finally could work, mow, etc. and then park and have a clean floor under it. That lasted about 9 months, and another showed up. It took some sleuthing but with some UV dye I traced it down to the input shaft (trunnion?), for the swash plate in the hydro. Now it looks like a major tear down of the hydro to replace the seal for that shaft. 2 questions I have is 1 the manual shows a wood piece to put the pump parts on the keep the pieces in order. Is it really that helpful? 2., What kind of wear could that seal failure be pointing to? I've often found what seems simple from the outside as in just a worn seal is actually from a root cause of other wear going on. Thanks!