Recently I've begun wondering about differential oil.
In 20 some years, the diff oil has never been checked or changed. ('83 300CD). The owners manual with the car says 90 weight oil, but nobody sells straight 90w, only eg, 85-w90 75-w* etc. Actually, NAPA will sell 5 gallon barrels of it, but not quarts.
What is typically used nowadays?

(Eg: I have always used in all my vehicles straight 30w motor oil as my climate doesnt need multi vis oil.)

-c-

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