My 250 has failed its annual inspection test (MOT) in the UK because the lights are pointing too far down. I can't seem to adjust the lights/lens. The adjustment screw does nothing and seems to spin without changing the direction of the lens. I note that many GM trucks had a plastic retainer nut on the rear of the light housing. Like this one:
Can anyone confirm if I am meant to have these retaining nuts to make the adjustment screws work?