I have recently hit a deer and it broke the top two brackets that are holding the headlight in place. The brackets are actually plastic and are integrated (plastic welded?) into the light housing. To avoid buying a new light, since there is nothing other than the brackets that are broken, I was contemplating to fabricate my own from aluminum sheet metal (which I have left over from some home remodeling) and screw them into the top of the light housing. My only concern is how to watertight the hole: are there small washer gaskets I can get or should I apply silicon or something third?
I would try to avoid drilling a hole in the housing. If you can epoxy the bracket to the headlamp shell. If you drill a few small holes in the bracket the epoxy can push through and will adhere better. Be sure the light is aligned before everything sets up.