Figured I'd post an update:
Dropped Kermie (wife's 2000 OBW) off down at the dealer. They dumped the coolant conditioner into it and let it idle for half an hour. The headgasket leak was still present, so under the terms of the recall, they replaced the headgasket on the driver's side only. Stopped the leak, and the other side shows no sign of giving out (yet).
Now the fun part: We didn't get to pick it up at the initially stated pickup time, since the mech. working on it had just finished putting everything back together, and discovered a noise. Not feeling all that comfortable with the noise, they didn't want to "release" Kermie yet.
Ends up that the cold start "piston slap" that I had tentatively diagnosed was evaluated by the dealer as the timing belt tensioner dying. The mech. was kinda flummoxed by it, since it would only show its age/failure when the car was started cold (real cold... like sitting overnight in 20-30 degree whether cold). Or apparently, if it was getting put back together after a headgasket job

.
So for the nice neat price of $270, they replaced the tensioner. Starts up like a champ now, no "piston slap" noise on start, cold or warm. The dealer made a big show out of giving me "half off on labor", but I was too happy that they had found it now rather than me finding it later (darn interference engines) to be concerned about the price.
Got another plus out of it, too... finally convinced the wife that spending money on an automotive stethoscope might actually pay out