Gear oil grade

What BMW actually printed is “brand-name hypoid gear oil, SAE 90 above 5 °C / SAE 80 below” — a type-and-viscosity specification for all three compartments, with no API GL number anywhere in the booklet. BMW-TD77 An earlier revision of this guide said “BMW specifies GL-5”. That over-stated the source and is corrected here. Hypoid gear oil of that era is what the API later codified as GL-5, so GL-5 remains the correct modern reading of the requirement — but BMW specified the duty, not the API class, and the distinction matters when you are weighing the GL-4 argument. The GL-4 argument — that GL-5's sulphur/phosphorus EP additives can attack yellow metals in the gearbox — comes from respected airhead specialists, not from BMW; run it as an informed owner decision if you choose to, but do not mistake it for the factory specification. If synthetic gear oil weeps at seals, return to petroleum — seals often recover. BMW-WSM7 §33 The 1981 sheet prints it in so many words: “hypoid gear oil, SAE 90, API class GL 5.” The owner-booklet era never named a class; from 1981 the workshop sheet does.