Greetings, Long time lurker here, I have used this site before to find useful information for my 5.3 and 5.7 GM engines. However, I have a odd transmission leak that is puzzling me. My workhorse truck 2002 GMC Sierra 1500 with the 4.3 5 speed transmission (NV3500) is leaking from the output shaft seal. I have replaced the seal correctly and the leak persists. It is not leaking from the front and only leaks when parked on a incline or after warming it up. The yoke that goes into the transmission was smooth and shiny, had very little lines or virtually no damage at all. The leak is very small, and really only leaks after a long drive. When I re-installed the seal I used a large socket and drove the seal in square into the housing. I also lubed it up with Synchromesh Gear oil, and some grease on the inside. I also used emery cloth and fine steel wool to fine-polish the yoke. I also lubed that with grease too (my chilton book suggested it.) The drive shaft has absolutely no play at all. nor does the yoke. The truck has 128k miles and I take the best care I can of it, having a leak I cannot solve is really frustrating. Thank you in advance, Chuck.