Fixing nut possibly too tight? With body preparation sealant excessive could cause local stress in light back-piece. Loosen nut to finger-tight. With the electric terminal properly fitted the light is well located in four places; the bolt, the terminal and the two locating pegs. Release the lock-tab and keep it out before removing or refitting the terminal. Support light with mild hand-pressure while refitting terminal or you will stress the light unit mounting. So far ours are all good (so far). Have added a dab of sealant to damp vibration.