With luck, we just found the problem with our steam vac. With a little more luck, we'll be able to get a replacement for the under-tank seal that appears to have mysteriously[1] gone missing. The frustrating thing is, now that we know what we're looking for, both of us have seen it lying around the house, but neither of us knows where we last saw it. And it doesn't appear to be available as a separate part.
*kick* *kick* *kick*
If only I'd recognized what it was and where it came from when I had it in my HAND.... now, I have absolutely no idea what I did with it.
[1] For values of "mysterious" about two years old and about 31" tall.
Update, 2004-07-13 2311Z
cymrullewes found the missing seal in the kitchen this morning. We have a working steam vac again! (We're still vacuumless, though, and the steam vac cannot be used as a general-purpose vacuum.)