Unfortunately you need to have it overhauled. It undoubtably must be the clutch pack for reverse which is a common failure.
This is also a problem that is best fixed promptly, if one wants the cheaper road of having that unit rebuilt. If the answer becomes a rebuilt MB unit w/torque convertor it doesn't matter.
The failure is such that as rev starts slipping the clutch material is mostly in the pan and filter. As the thing starts singing and catching the frictions are metal to metal and the resulting mess goes everywhere. The damage is easily fixable but the mess can get into the valve body, governor passages, etc. and come back as eternal shift irregularities.
Bosch Master, ASE Master, L1
33 years MB technician