The reason I mentioned a converted system is because R134a runs at higher pressures. I ran into this with my Civic when I converted. I had to replace no less than 2 o-rings that decided to give way, along with an evap., a hose, and a pop-off valve on the compressor. Since Hondas aren't usually prone to that kind of trouble, I figured the changover was the likely culprit.

Make sure your mechanic isn't trying to use the sightglass to check if it's full, because you can't do that with a dryer on R134a, only R12. He has to know how much refrig. to put in, period.

You also may want to check for sure but I think the o-ring mat'l is diff. with
R134a too. I've been told that R12 o-rings will eventually fail on R134a.

Some mechanics have a "sniffer" that they can poke around with, and a buzzer will go off when a leak is detected.