Jerry,
There is no other way to find a leak in an ac system, other than an
electronic sniffer, or the dye system.
If you have a slow leak, it's sometimes impossible to detect.
Besides, a poor o-ring seal, it could be a thousand other things that
are causing the loss of freon.
An older hose will leak slow through the pores of the rubber.
The condensor could have a pin hole in it, on and on.
So, if you have a slow leak, and you have put the dye into your system,
be patient, it will show up eventually.

Good Luck,

Terry