My '79 300D's trans acted wierd last week. It was not engaging until higher RPMs were throttled. Even then it was a bit weak.
So after checking the vacuum lines, linkage, fluid dip stick (pink, no graininess, no burnt color or smell), I had it towed to Peter Schmid Transmissions (MZF-Bayer, Inc.) in Burlingame, Ca. (south of San Francisco)

They are a very reputable and honest business specializing in Mercedes transmissions.

I got it back with a 'whew' because I was worrying that it might cost more than the car was worth to repair.
It turned out to be a "sticking valve in the valve body".

Very reasonable cost to repair and the car is back on the road.
Any other 'shop' could have taken me for a ride on this one !

So, if your trans has symptoms, it might be the valve !

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD