Re Rotax switch, you can spot braize the worn out key slot, then drill and file for the key profile. This area is always torn out, and this is what I did to restore mine. You can then chrome it as this piece is easily pulled out its just pressed in. Be careful. Re broken switch arm the other option is to buy another later one and use that part. Bakelite can be filled with coloured araldite.
Have repaired the broken part with Loctite super glue and it's a good strong bond which would probably last longer than me. The key slot is also receiving attention with parts from a Austin 7 donor PLC switch.