That model was known for it's limited brakes to the best of my limited knowledge. I would scour the antiques section Called pre 1979 models or whatever for any way that has come about with time to improve them generally.

I know this is not the best response to your question but few on this site in the diesel section would know much about them in my opinion. I never worked on one but was all too aware of this issue. What was strange to me is otherwise mercedes usually put good brakes on most of their models.