Higgs Boson wrote:

Thanks to other inquiring minds for ingenious comments.

I should point out that the leakage occurs AT THE BASE, not the top,
so I doubt if it's what hr (Bob) suggests, but will keep in mind.

Aha! moment! Ed suggested wrap in paper towel and look for spot.
Might indeed be the way to isolate a crack or other aperture not
discernable to the nekkid eye.

Will report back when results available.

HB

After trying the paper towell idea and finding the leak source, maybe this
will work:

Completely rinse and clean the inside with hot water and allow to dry
completely. Then use Super Glue -- the liquid kind, not the gel kind -- on
the inside and swirl it around as much as possible. I have used Super Glue
on hairline-cracked toilet bowls and even toilet tanks and have had it work.
It seems to get drawn into the crack by capillary action and then dries and
seals the cracks. Or, maybe some type of clear and thinned polyurethane
sealer on the inside will do the same thing.