I had on-going P0011 issues. At some point, I realized it was the anti-drainback valve allowing the OFH to drain, which in turn led to low oil pressure on startup to the VANOS. Symptoms were the red oil light stayed on for a few seconds on each start (like a normal car would, after an oil change) and freeze frame of the P0011 showed it triggered at or right after startup.
Normally, one would just change to a new housing and change it again, when it fails. I am cheap and decided to try the anti-drainback valve replacement. I bought mine off ebay, from the Ukraine, for $30 shipped. Yes, the same one that is at war with Russia, but it still arrived in 9 days. It comes with a new OFH gasket also.
Valve supplied without a spring. The spring is necessary to take out the old valve. to ensure correct operation of the valve. M50TU, M52, M52TU, M54, M56 BMW E34 E36 E38 E39 E46 E53 E60 E65 E85 11421713838 11421738640 11421722513 11421738639 11421740001 BMW plant is not sold separately, but only...
No instructions come with it in the box, but ebay listing (and the link above) showed a picture of using pliers to pull out the old unit, then installing the new unit, after lapping the plunger to seal surface. You reuse the spring from the original drainback valve. It's a really tight fit, so I ended up drilling sections of the original valve, until the rest of the old valve fell out. Original valve, mangled, but out of the housing:
Here you can see the grooves that the stock plunger eventually grinds into the housing, which is one of several reasons why it was no longer functioning:
The other issue with the stock design is that the plunger is too short. The Klifex design has a longer plunger which goes into a guide hole, keeping the plunger from dropping back in off-axis, when oil pressure is absent. Additionally, the replacement has wider plunger fins to spread the abrasive force of the plunger, as well as a better sealing surface shape.
If I remember. I'll report back on how well it's holding up.