Seamaster 120m Plongeur De Luxe Crown

This is probably a very silly question, but does anyone know if the Plongeur De Luxe has a screw-down crown? I haven't had cause to adjust it from the crown in months, and seem to recall that the crown screwed down last time, but this time it doesn't seem to want to screw down. The watch is 39 years old and, as far as I know, totally unserviced, so it may well be damaged/imperfect. I'm not planning on taking the watch near water - I'm just curious as to whether I'm mis-remembering