...those of you with M54-powered BMWs, that is. If you're active on the BMW boards, you'll know that the factory VANOS seals were made from a material that degrades in the presence of oil; not exactly a good design decision. While BMW has decided to do nothing about this, a third-party company (Beisan Systems, in which I have no financial interest (end disclaimer)) now produces updated seals made from more appropriate materials.
Having recently done the work on my 525i, the difference is nothing short of astonishing. The idle is smoother, the power below 4k is notably better, the intermittent off-idle stumbling is gone, the engine is quieter throughout the range, and the oscillating idle when cold problem is completely gone. I did not even realize how pronounced these issues were until they disappeared.
Beisan has an excellent DIY on their site. It took me about 4.5 hours to do the swap. Those with single VANOS can upgrade as well, but special tools are required; double VANOS can be done with basic hand tools.
This is one of those jobs I never would have put off as long as I did had I realized how big a difference it would make. Do it. Now.
