Valve cover oil leaked, then Mass Air flow sensor issues?

[paepaesano]

Bought a used 2007 650i with only about 55000 miles on it. Was very clean, Car faxed, saw results of dealer prep and computer check of engine before purchase. About a year and 6000 miles later: Oil blew out the valve cover. It was a sudden leak after a short drive with an oil film on the passenger front wheel and down the side of the car. First, had both valve cover gaskets replaced. Car returned to me. I think I paid a fair priced for work. One week later, service engine, light on. Mechanic had car 4 days, "found codes for rich engine idle, clear codes, performed adaptation and reset of Engine ECM". Paid a couple hundred for this. Got car back because I was going away for 6 seeks, only drove it a short distance home and put trickle charge on battery. Came home, first drive, 50 miles, service engine light back on. Mechanic had car a four days again. Claims he kept needing to diagnose, tweak, clear codes, and then drive 50 miles and then light comes back on so another day shot, so repeat, repeat.. Vacuum leak somewhere?? Then, after 4 days, says he just realized, someone installed a KN performance aftermarket air filter. This is likely causing engine codes to keep tripping as computer is trying to adjust to non OEM aftermarket filter. Also, he has been "in communication with BMW" as he said before he has all up to date software and BMW assistance "package". Another day or so, "soft" engine code in his computer, rich/lean mixture problem. but "service engine light not on yet". Wants to replace Mass Air Flow Sensor. Says it is likely the aftermarket filter had residual oil from filter manufacturer. I still do have car back after a week, and I OK'd installing new OEM BMW air filter and Mass Air Flow Sensor.

Anybody out there ever have a problem with non OEM air filters causing engine code trips?
Is it possible that the oil leak (blew onto the passenger front tire and spread down the side of the car) got into the intake a caused the problem?
Should I take a firm stand with the mechanic that I should not pay for all the added diagnostic work and vacuum leaks and problems because it should have been resolved when he returned the car to me with the new valve cover gaskets?
Could the MAFlow sensor be cleaned instead of replaced?
Do you think I should be looking for a new mechanic??
I appreciate any comments,

[Timm]

If you really had a valve cover gasket blow out then your crankcase ventilation system is blocked - there should be a vacuum of a few millibars. More info here:

http://www.meeknet.co.uk/E64/BMW_E63...eplacement.htm

http://www.meeknet.co.uk/e31/BMW_M60...entilation.htm

I just re-did this job today and noticed that the RHS bank (with the separate PCV) had a partially blocked vent pipe from the valve cover - I bet yours is completely blocked. The chances are, as I found the first time I did the job, that you have a tear in one of the diaphragms, this will let in unmetered air and cause mixture problems.

An oil-covered air filter can cause damage to the MAF - fortunately they are cheap and are a service item just like the filter, so get a new one fitted and take it from there.....