4000Q that won't start after a good rain?

[John <jb@access.digex.net>]

Please help!  My '85 4000Q is getting harder and harder to start.

In the morning after a rain, the starter seems strong, but nothing
else happens - except that after after 5 seconds of the starter turning,
I hear a small thump or clunk.  When I release the starter, sometimes
I hear a tiny hint that it might be starting, but that's all.

I tried DRYGAS twice, and after a couple of hours it started.  But once
I just waited a couple of hours without DRYGAS and it started.  But lately
it's been raining a lot and I haven't driven my Audi in 2 days.  I am trying
DRYGAS again this morning.

I tried jumping it (more volts) and that didn't help at all.  A visual
inspection also turned up nothing obvious.

Some of my vaccuum tubing is a bit old - can a vaccuum leak cause this?

Why does it seem to happen after a good rain!?  All suggestions welcome!

Thank you,
John