[Arran]

George;
I don't know if this has one or not but quite often controls, and switches have a "C" shaped clip holding the shaft in place, if you can carefully pry it open with a small screwdriver, and extract it, that will allow you to get more solvent into what looks like a rather tall bushing. In fact one you get it loose you should be able to tap or pull the shaft right out of the bushing to give it a good cleaning, though you will want to file, or polish off any burs caused by the pliers.
Regards
Arran