Does the engine brake feature work in reverse? sounds like a problem with the K2 clutch to me, that's what produces the shift into 4th and holds the gear. Sometimes the teflon seals wear a groove into the clutch drum, which would cause need for replacement, also the rubber lip seals can go bad, especially when it sits for a long time.

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Alex
MB Star certified, now independent.
Owner/Operator FDMotorsport Mpls. MN
Mercedes and GM certified transmission rebuilder
We all need a little help sometimes...

1998 E320 4MATIC-- stolen by my sister
1989 300TE-- sold
1999 C230 Kompressor