Jon Elson wrote:

I dropped the cap for the service valve. This is the
thing with about a 3/4" hex and a cylindrical dome above it, that seals
the
valve stem of the service valve.
Well, my friend came over with his metal detector, and found it in just a
couple minutes. So, all is well again, and the charge should hold for
another 10 years or so.

Thanks, everybody,

Jon