So, there's still a slow leak (a drop every once in a while). Possible causes:
1) new bolt not tight enough (I was afraid to put any pressure on it).
2) I used two copper washers instead of one, because the new bolt is a
millimeter or so longer than the old one (should I be concerned about this
length?).
3) the newly threaded hole just isn't strong enough
4) something else I haven't thought of.

Solutions:
I'm going to reinstall the plug bolt using a nylon washer, which should
form a better seal than the copper ones that VW has been giving me. The
washer is made for this kind of application, so it should be OK.
If it still doesn't work, I have a rubber expansion bolt as Bob described
in his sermonette (thank you Bob!). I hate to use a solution like that (it
_seems_ like such a temporary measure), but it'll do until I find a better
solution.

Possible original causes of my problem (what did I do wrong):
1) I don't think I used too much torque on the bolt during my oil changes,
but since I haven't used torque wrenches to tighten this bolt, I can't
really claim any exact torque figures. I tend to use a six inch socket
wrench and hold it close to the neck. I'd say I tightened it to 15-18 ft.
lbs. at most, but that guesstimate's worth zip in the absence of an actual
measurement.
2) (this is the biggie) You may gasp in horror at my stupidity, but I'd
always been taught to warm up the engine a little to get any gunk up into
the oil (so it drains out with the oil). I'd always wondered about this,
but it always worked. However, warming up an aluminum engine and then
pulling a bolt out of a warm crankcase may win me new honors in the
"no-brainer" department--literally. This theory may be supported by the
fact that the bolt stripped coming out of the case--not going back in.
3) I've been using new copper washers, but Bob's sermonette reminded me of
the old crushable washers I used to use on my 412's (Type IV engines in
Type IV bodies--what a concept). Maybe these washers contributed to my
problem, although they are what's sold at the dealer. I haven't seen the
crushable kind for years around here.

Hmmmm.
Hope this helps someone on the road to a similar mistake,

Dave

=====================================
dlm202@psu.edu
Dave Mancuso

'87 Vanagon (Kalypso)
'89 Jetta