I agree JackD, and I had already done the search on "oil" and found a lot of ideas - not all very practical or safe by my standards.
My problem was I could not find - or maybe missed it in the 95 manual - what oil was actually recommended. The original owner used Castrol 20W50 at the MB 7500 intervals assumed.
If that is not recommeded I'll be quick to switch. This is my first diesel rodeo and I know soot can be a problem.