It makes sense to change the tranny fluid and Gear oil to synthetic, since they will last a lot longer than motor oil, and will not decompose due to the excessive heat of the engine.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)