One place I have used in the SF bay area and was quite impressed with is:

KarmaKanic (Steve Nechodom) (510) 548-4494  2503 10th Street Berkeley, CA.

This is a one-man shop, but Steve KNOWS Vanagons. I took my Westfalia in for
a clutch replacement, and he went over the entire van and reported on its
entire condition.  In talking with him, he definitely knew all the quirks of
the vanagon.

Todd Last
'88 westfalia.