[W126 Coupe] Vibration on acceleration and tranny servicing

[rcl]

My 1987 560SEC has developed a vibration on acceleration - about 
1300-1700rpm in 2nd it vibrates through the drive train and I can feel it 
through the body of the car. Outside this range all seems perfectly normal. 
Gear changes are still smooth, although when cold it seems to take a while 
to cycle between D and R.

One mech didn't really look and said the tranny was stuffed - the same guy 
told me that 90k (miles) ago - so I'm not sure he knows, or he is trying to 
scam a tranny repair for one of his buddies - any  thoughts ?

Also, there seems to be 2 camps on transmission servicing - those who say do 
it regularly - fluid, filers etc. And then those who say never touch it 
(especially not fluid changes) unless there is a problem......what is the 
view held here ?