More than likely the LB3 clutches are worn out, actually that is a safe bet.
LB3 clutches are for reverse only and are located behind the front pump housing surrounding the K1 drum.
Transmission has to be R & R to access. remove the filter first, open and inspect for clutch and metal material. If present trans has to come apart.
Mercedes-Benz Master Guild - 2 years
Shop Foreman - 20 + years - dealer.
Part owner - MBZ Transmission remanufacture