The only answer I have is to rebuild your BENDIX.
I suggest you rebuild both of them at the same time.

Here are the kits.
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

Here is the hone I use
1-1/8" Brake Cylinder Hone

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__________________
ASE Master Mechanic

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D

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