Matt had complained about stalling and some lumpy power delivery at low RPM which is almost always a sign of failing VANOS seals on these cars. BMW used o-rings that tend to get brittle with age and they don't seal well, causing oil to bypass the pistons and not actuate the cams properly.
With the VANOS unit off you can see the covers that retain the pistons.
With the covers removed, the pistons come out. You can see the o-rings, which are a square cross section. There is also a spacer beneath these that takes up some of the depth in the piston groove.
When the seals are bad it's very easy to tilt the piston in its bore, not a good sign.
The only way I've found to remove the seals is to cut them with an X-acto. There are aftermarket kits to replace the seals with a more resilient material, so as soon as those come in I'll replace them.
