Hi Graham
if I am understanding your post correctly,it is the two red reflectors you are referring to and not the actual light clusters ?
If so ,it is good news

The rear reflectors have a central screw thread on the back of them and simply screw in to the ash frame.I can't actually remember which way to turn but, going by -
'righty tighty,lefty loosey' I would assume it is anti-clockwise to loosen them off.
If they are really stuck tight they may have to be sacrificed to get them turning (i.e..
'Billy Bodgered' - small chisel tapped in the rim 'till they start to loosen

) ;new ones are available from the usual suspects if this is the case......
HTH, James