Bru,

The next thing you can do is replace the B2 piston black bore seal which is hard and brittle is more than likely your problem, but most if not all shops will not do this kinda work.

http://www.dieselgiant.com/Mercedesb2pistonsealreplacementl.htm

Nulu,

These old transmissions are typically good for 100k to 150k as they just run hot. Reverse will delay as the reverse lip seal starts to tare, and eventually you get this roller coaster clunking sound. Then you loose reverse entirely...To fix reverse, one has open the transmission from the front, and some have gone in to fix reverse, yet the best solution in the future is put an external cooler on the transmission-heat kills all transmissions-A cooler will multiply the life of the transmission by a factor of 2 to 4 times.

Here is how to do the job...

picture 7 -the inside seal is the culprit

722.5 transmission oil pump rebuid DIY - Mercedes-Benz Forum

no reverse / jerks in reverse when cold - Mercedes-Benz Forum

All the best,

Martin