Sheared stud pressed out in a vice with a small socket over the head

Cheese-head screw of the same thread, with the lower half of the head filed into a square

Open out the hole a little by bowing it downwards with the square tang of a file, insert the screw, then use the 1/4" drive end of a socket, which just fits over the square shank, to press the base-plate back down again which pinches the screw up tight. Repairs such as this give a level of satisfaction out of all proportion to the time and effort expended.

Refit with Waxoyl smeared over the back of the light units and threads.