I replace the reverse frictions in 722.2,.3,.4,and .5 all the time.

I buy and sell old MB's for a living. We encounter reverse friction failure all of the time, mostly in heavy cars like the W140 and especially the w124 wagon.

It's an easy fix. Have the trans pulled. Go to a trans parts supplier like DACCO DETROIT and get the five friction discs (they are asbestos lined like a brake pad). Pull the torque converter out and remove the front pump. The reverse frictions and steels are behind the front pump.

Takes 15 minutes or so after trans is pulled. We ususually buy the re-seal kit and replace all the front pump o-rings when we do the job.

The frictions are like $2.50 each from a trans parts supplier (and $35/ea from MB), the reseal kit is about $90 or so for all the rubber in the trans.