Nuevo Classic Rear Lights

There are 4 screws holding the lenses on, with these removed the lens is reluctant to come off. Anybody come across this before on a Nuevo,or Lancashire etc ? 
Is there an O ring seal between the lens and light fitting?

4 screws on the outside suggests it DOES pull off, however, usually there is a rubber/foam seal in a recess & they can stick to each-other, try finger & thumb, top & bottom & pull/wiggle at the same time, usually gets 'em off. 

Cheers, will let Brian know they are in Europe at the moment with infrequent visits to the forum

Had same problem and discovered previous owner had sealed it with clear sealant that was a real pain to remove.