Bernie,
I had something similar recently. Had a fuel leak. I pressure tested the
lines and they held 100 psi. Next pre-flight - leaks. Disassembled &
reassembled regulator. No leaks. Next preflight - leaks.

Bottom line - my steel braided fuel line had apparently carried high current
at some point. There was a dark spot which eventually showed a fine jet of
fuel when under pressure. New fuel lines. No more leaks.
Hope this helps.
John