Originally posted by rpriedhorsky I hear you!
Regarding the glue, you might consider hot glue. That might be easier to remove if/when you want to sell the lens. I'm not familiar with the other type of glue that was suggested.
Hot melt will work, but be cautious of how it is applied. The metal must get hot enough for the glue to adhere, but not so hot that the glue runs under the sliding switch; if it does get under the slider, removing it might be a challenge..
I suggested Devcon Plastic Welder (in a double black tube - hardware stores, Walmart, etc) because its working properties are just right for this job. It will adhere to the clean lens surface, has enough body it won't flow under the sliding switch, and is strong. It will be removable if you try hard enough to pop it off.
Other adhesives will work ok; one candidate is black fingernail polish. Put some wax under the slider to fill the gap, clean the metal close to the slider with nail-polish remover, then apply a few coats of black nail polish waiting for a coat to dry before applying the next. In the future this can be removed with nail polish remover.
Almost any glue will work if you don't care about returning the lens to its original condition - let the glue applied run under the sliding switch.
Dave