There are no typical concerns. If a part shows a leak when syn oil is introduced, there was an issue there far earlier. Fix it!

Back around 2001 or 2002, there was a set of photos on here that showed the internals of a 300D diff on regular fluid and how running M1 cleaned it up substantially over a few thousand miles. Good stuff.

I'd be running syn. M1, Amsoil SVG, Royal Purple or equivalent.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)