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The BMW TSB SI B11 08 98 regarding engine oil for M engines calls for "Castrol RS SAE 10W-60 Synthetic Oil also called Castrol TWS Motorsport SAE 10W-60 Synthetic Oil".
The Castrol RS is the pre-2000 formulation. After 2000, the Castrol RS product was reformulated and lost its BMW approval.
According to Castrol, EDGE 10w-60 is the same as TWS.
As Blacklight says, Castrol RS SAE 10W-60 Synthetic Oil, also called Castrol TWS Motorsport SAE 10W-60 Synthetic Oil, also called Edge 10w-60 has a higher film strength than other Castrol 10w-60 products. I have read that the BMW Approved product is ester-based (it's a direct competitor to ELF and Motul ester racing oils) while the non-approved formulations are PAO based.
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