The costly E36 mistake is filling the gearbox with 75W-90 gear oil — don't. BMW specifies ATF (Dexron III) or BMW MTF-LT-1 for the Getrag and ZF 5-speeds behind both the fours and the sixes.
Capacity is small — roughly 1.1-1.3 litres for the smaller Getrag boxes, about 1.7 quarts for the ZF S5D in the 328i and M3 — but fill to the level plug, not by volume.
Red Line MTL or D4 ATF are popular alternatives
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