My E23 picked up this bug last week. My trans guy says it is pistons in the valve body. Good luck. BTW I havn't fixed mine yet - I just drive one of my others.

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Good - Fast - Cheap: Pick any two.
Current:
E23 735i; E30 318i; E32 735iL; E38 735iL; R50 Cooper; R55 Cooper Clubman.
Previous:
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i