The fun never ends: 2002 Sonata GLS slow leak in A/C somehwere. Is it worth using stop-leak stuff?

A while back I posted that I recently discovered my A/C doesn't turn
on. Apparently due to my freon having leaked out. So my mechanic says
I have a slow leak somewhere. He checked all the accessible lines and
it doesn't appear to be on the outside. He said this leaves the inside
under the dash. Fun fun fun. So he says there's this new stuff on the
market that might help stop the leak if it's introduced into the
system. Anyone have and experience or luck with this stuff? Is getting
at the A/C stuff in the dash (condenser et al?) easy or does it
require the dash to come off and 20hrs of labor? Just checking my
options in case this stop-leak stuff he's going to try doesn't work.
Thanks for any replies.

- Thee Chicago Wolf [MVP]