[Arran]

Be careful in cleaning the dial on your American Bosch, it may have "washaway" in or paint on the back. I don't know what to suggest to safely clean it, on the beige coloured plastic Philco dials mineral spirits are the safe thing to use, but those are made out of a phenolic or celluloid based plastic, not glass. I have a Canadian cousin to your Bosch called a Northern Electric, and it has a very similar dial, so I will have a look at it, and report back later about the dial scale and the pointer/s it has. If you can look around the rear of the pointer shaft see if it has a set screw or something holding it in at the back.
Regards
Arran