Run it a few more days, or until the refrigerant leaks out, then try again with your UV light. Check around the compressor pulley where it would sling out on the pulley. Check everywhere you can get to and wait 'til you can get some condensation on the ground, preferably at night to check the evaporator.
Patience my friend.
I don't know how hard the evaporator in a 126 is to do. The 124 is near impossible, the 123's are difficult and the 201's are a piece of cake. I don't know where your 126 falls. I'm sure someone here has done one and can offer a reply.
Keep on checking with that black light, preferably after dark, you will find the leak sooner or later.