[Dangerous Doug]

Thank for the advice. After experiementing with soap and the original o-ring, along with soap with some smaller o-rings, here is what worked for me:

The diameter of the original o-ring is 0.135". This pops loose, even with soap. I purchased a handful of smaller diameter o-rings. 0.100" falls in---and subsequently, falls out. In my collection of o-rings was a 0.075" diameter o-ring, with a smaller overall diameter than the original. I put this one on first, stretching it to get it over the cap mount. Then, I added on top of it the 0.100" o-ring---properly soaped up, of course.

This pushed in, and then with a twist I could hear a light sucking sound, and in she went. Seems stabile, but I'm sure I'll find out tomorrow when I get in.

In terms of the soap, what I used was some glycerin soap from the house. Not sure if that was the right kind to use, but I wet it and rubbed it all over my hand. Then, I squished the loose o-ring around in my hand until it was soapy.

Anyhow, it's on. I'm happy.
DD