1994 Chevy Camaro Mysterious Leak

My AC won't hold a charge. Lately, a cahrge will only last a day or 2. The mechanic says he can not detect any leak. He now believes it is losing the charge suddenly rather than continuously, through either the condenser or the evaporator, as they contract/expand and open a crack. He suggests getting a condenser (in case it needs to be replaced), removing the condenser (at which point he should be able to see if it has dye on it0 and replace it if it is the source of the leak. If thats not it, try the same with the evaporator.

He's already replaced several parts because they were leaking, but now says they were small leaks and may not have been the main problem. He says the condenser and evaporator are the only parts he can not see unless he gets them out.

I don't mind going thru this if it is likely the problem, but I'm having a little belivability problem right now.

Any help is appreciated.