Loss of freon in A/C system.

For 2 years I have been adding cans of freon (with stop leak). I fill per year was good for one summer.

Now a fill lasts only a couple of weeks. I took the 2016 Odyssey too a repair shop that did a pressure test on the system. They found no leaks. They suggested I do a fill with dye and check all the tubing and compressor with a U/V lamp.

Looking on Amazon for a U/V lamp I saw they also sell a freon detector unit. This looks like it would find a leak more readily than the U/V.

Any thoughts on this (and also a permanent fix) folks?

Thanks.

Geoff N