Why? Never heard that. I know DOT5 is incompatible. But you can mix DOT 3 and 4. I believe Castrol is DOT4. So how does it work when you initially bleed the SRF into the brake system that has non-SRF fluid? Some of the old fluid will mix.
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2018 F30 320iX Melbourne Red
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red
2000 E36/7 Z3 Steel Blue
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