Get the mighty vac. A good book is from **************.com for trouble shooting. Took me all summer on and off to repair my door locks. Turns out it was a broken vacuum line. Also some good diagrams right from the forum here.

Be methotical, draw scetches, keep and do not throw out your notes. Take your time. You will learn your vacuum system for sure.

Tom Scordato
1977 300D
1979 240D