Use SAE 75W-90 hypoid gear oil to API GL-5 in the E36 final drive — about 1 litre, filled to the level plug rather than by volume.
If the car has the factory clutch-type LSD (all M3s, some others), it must be a friction-modified / LSD-rated 75W-90, or you add BMW's LSD additive — a plain oil makes the clutch pack chatter on tight turns.
The 328i and M3 run the larger 188mm case; lighter models use the 168mm
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