Actually, go find an A/C tech that uses a "sniffer".
A sniffer is literally and electronic nose, which can have the sensitivity changed.
On my older vehicles I found an AMAZING mobile A/C repair guy. The guy worked on automotive A/C for years and used every method known to find refrigerant leaks. He said his life improved 1000% when the sniffer was made available. No more dye's, no more lights, no more missing leaks. He was able to find the smallest leaks that other shops couldn't.
Example: I had an old Mazda pickup that would constantly loose it's refrigerant, with no sign what-so-ever. Every year, I would go to a different shop, they would put the dye in and they couldn't find the leak. This went on for 4 years
I finally gave this guy a chance (I was reluctant because he was literally half the cost of the "Pro" shops) and he shows up at my house, tops off the refrigerant, and goes to work sniffing the A/C lines.
In less than 10 minutes, he finds TWO leaks. One at the compressor, and one at the inside exchange. Unfortunately, the compressor was to far worn out and had to be replaced. So we upgraded my truck to R134A.