Having spoken to a turbo specialist, he advised very strongly against flushing the engine with any form of detergent or adding any kind of additive to standard oils. The reason is the tight tolerances on a turbo, any foreign object can cause blockages, and oil additives close up the tolerances. As for the oil separator, I took mine off my 1996 R, flushed the separator, and also cleaned the connection down by the turbo where the separator feeds the fumes back into the inlet, and no more excess pressure problems. The bigger problem on my car was not the separator, it was the other end by the turbo intake.