300SDL transmission, ever replace/repair one?

[Oil_burner]

Looking for advice on whether or not to consider tackling a transmission on my '87 300SDL. It has less than 100k on the clock. My indy thinks that it has problems with the planetary gears (see earler posts). From people here and others I have talked to at two MB dealers it is more likely the front pump. One service manager said it could even be just the seal - says a pump that is "starved" for fluid can whine. It is leaking fluid fast - about 1qt/10mi. It whines even when not in gear. Not real loud, but a very noticeable whine. Otherwise shifts just fine and seems ok. Yea, yea, I know that is a huge leak; it is not being used right now.

I figure worst case I get it off and have to replace it with a rebuilt. This is my backup car and I am not in a big hurry. My indy has had it now for 3 weeks (yes three); and has not yet got me a price. The stealership say he would do it for a mere $3500. Anybody out there ever replaced or repaired one? How difficult is it to do all of the adjustments? Special tools needed? Please share how much of a pain it was. Thanks.