Links to Other Resources
The ABC is a go-to place for support, with it's own mailing list. Nearly every airhead expert left in the world posts there. Membership is $25-50 per year (depending on where you live) and gives access to the info pages in the web site, as well as a subscription to their monthly magazine. If you subscribe to the email list, you can search the email archives here.
Robert Fleischer's canonical airhead information website. This is a treasure trove with details on maintenance, oil chemistry, ignition timing, carb rebuilds, you name it. Unfortunately it is hard to find things unless you have spent some time poking around. Many of the articles are linked on his References Page. Other important pages are at Torque Values,
Anton has a ton of experience with a variety of BMWs, and shares a wealth of info in this well-organized site, for example this definitive article on oil filter installation.
Tons of detail about airhead work, repairs, disassembly, improvements, and how-to's like "how to diagnose a low oil pressure light".