I think 5.0 resto sells a kit to reseal you headlights. IMHO if you are going to do all the work of taking out your headlights and crack them open, might as well buy a new set.
I can't see that drilling a hole at the top would do anything but let water in. Seal the top hole with clear RTV and drill one in the bottom.
An alternate idea would be to seal the current hole, and then remove the lens assembly. Submerge the lens in a bucket of soapy water, and try to blow it up like a balloon. You won’t develop enough pressure using lung power to damage the lens, but you might find the leak.
All you have to do is take the headlight out of the car. Take a blow dryer and blow dry the moister out of the headlight, should just take a few minutes. Then use a clear silicone to seal the outside edges of the headlight, all the way around. Works great and mine never leaked again, still going after about 7 years later!!!