Evidence of oil in the clear in-line filter in the vacuum line, I bought a RONAK brand shutoff valve from a local parts supplier and had an indy (afraid to do it myself in case of a run away engine) do the re and re. The indy charged me 1.5 hours of labour only as I had supplied the part. Fine. Well, that was only three months ago and I have the same problem. I have now purchased a BOSCH brand from the MB dealer and installed it myself fine.

My cost breakdown:

Ronak brand shutoff valve - C$ 80.00
Indy labour charge - 140.00
Total C$220.00

Bosch brand shutoff valve - C$ 92.00
DIY (2 hours) 00.00
Total - C$ 92.00
Less refund on Ronak 80.00
Total - C$12.00

Lesson learned: For long-term benefit it pays to buy and use OEM parts only.