I have a few mounts that hold HEAVIER components out from the bike far enough that the shock of road irregularities(increased by the long-mount leverage) works the screws loose. Loc-tite doesn't help.
Best example of this: I have a 2 D-cell tail light (Brit-style head lamp with substituted red lens) mounted to a seat stay clamp-on. This clamp has an additional screwhole with a pointed screw for grounding the lamp circuit & I suppose keeping the clamp tight. Digging a hole into the seat stay of my one owner DL-1 is UNEXCEPTABLE. So I eventually I tried wrapping the stay with a piece of INNER TUBE RUBBER. The rubber acts as a shock absorber (and somewhat like a lock-washer) and now the screws never require retightening.
This ALSO works to eliminate rattling for racks & other after market accessories that don't fit exactly right.
Calvert Guthrie
Kansas City