Yep, Tim's on the money. Plastic and rubber bulb unsrew, can be quite stuck together. The switch can be pried open and cleaned/lubed.
You "can" drill out the rivet, disassemble, and make a new one, but as noted I just masked and painted. You can mask the switch box and do a silver/grey and balck eslewher to get "close". To remove and replate would be a PITA...
I think the rubber bellows is now reproduced, not sure about anything else.