Quote:
Originally Posted by m3heaven
What 6MT transmission and diff oil is everyone using in here?
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It's up to you to decide how much weight you put on OEM fluid approvals. BMW has very strict requirements to ensure high-quality fluids are used that can handle hard use, high temps, won't break down, etc. That being said, some blenders might decide they don't want to spend the money getting the OEM approvals (they're quite expensive). Red Line, for example, takes the approach that their reputation outweighs an OEM approval. Does their stuff meet OEM approvals? Maybe.
The OEM Castrol fluids are a great choice too. We know they've been tested and validated for the M3 and will meet BMW's requirements. But you also have companies like Motul who have race-proven products and put more focus on a specific use case.
Everyone's car is a little different as is the usage. It's hard to make a blanket recommendation until you actually get the fluid analyzed. I don't think OEM is a bad choice, but you have a lot of reliable race-focused fluids if you're willing to spend more and run shorter intervals.