> i've done this a jillion times on other vehicles -- another secret VW handshake?

With me its just the other way around: had this problem with other
vehicles but not with the Vanagon.

The trick is sometimes crud and rust can plug the bleed/drain holes. If
you remove the bleed nipple completely and poke around inside with a
bent paper clip you can dislodge the crud enough to drain it and
hopefully flush out the crud. 

Larry
'86 Syncro Westy