"Bob" wrote
It's not a very long run, but I really don't want to rip away part of the
ceiling and wall to try and find.

Thinking of having the A/C guy, or a Plumber just run new tubing on the
bottom of the existing ceiling. Tubing would be exposed, but would paint.

Question: good idea or approach ?

Would this new tubing have to be insulated ? How ?

BTW: are leaks in the connecting tubing fairly common after 20 years or
so, or is nearly "always" a leak in the compressor or elsewhere in the
actual A/C unit ?

Not a good idea. Have an AC tech come out and find the leak, if that is the
problem. It is not a simple matter of a plumber running new tubing as you
would for water. He will have a leak detector and can probably pin-point
the leak in a short time. Lines have to be evacuated and charged and must
be done by a licensed operator.

It may be something simple like a loose compression fitting and it is
repaired and the system re-charged. Figure any house call is going to be
$100 minimum though.

Some jobs are best left to a pro. This is one of them.