First do not try a stop leak unless you want to chance ruining the system. This stuff is junk, I personally have seen it ruin compressors. Now if you want to check for the leak 2 ways to go about it. First put the car on a rack and stick a leak detector in the drain tube. Normally you will get a funny smell from dash vents (if 134a) Second ( how I do it for warranty companies) remove blower motor and you can stick a leak detector right on evaporator, (I use a boroscope I have) If it comes from the drain tubes then 99% evaporator leak. Labor time on this is 23.5 hours. That includes replacing evaporator core, reciever drier and evacuate and recharge.
