How about you just get a new pinion gear from one of the reputable manufacturers. Then clean the set screw, and threads in the pinion with some solvent. You see any manufacturing oil or contamination will chemically alter the loctite, which renders it useless. Also in all likelyhood the threads on the pinion that is giving you problems are damaged, which prevents the loctite from curing to full strength. The way I look at it my time is worth way more than the cost of a pinion, so to go through all of that effort just to save a few bucks seems stupid to me. So, if you have the right tools, you could add a second set screw, but the overwhelming majority here are going to say replace the pinion, because that is the smart and easy thing to do. If you are dumb, or like doing things the hard way, then by all means, drill that hole.