Same thing with my 1995 E320. Reverse became very shy, then quit. That was @160,000 miles and 7 years ago. It was the reverse clutch, it happens to most 722.xxx transmissions. I did the rebuilt thing with Adsit For about $1600.00 exchange and
i'm thinking that included a rebuilt torque converter to go with it. The new trans. has gone 60,000 miles so far without a hitch or a leak. Fluid looks great. Go for it. Get a rebuilt transmission. My mechanic charged 4.0 hours to do the job.

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Edgar