Had a fuel leak - ended up pulling the sender unit out. The fuel gauge needle has always jumped around from zero up to where it should be. There's a brassy metal strip about 1/4" wide from the potentiometer up to inside of the flange that bolts to the tank where it attaches to an insulated bolt that the wire to the gauge connects to. The metal strip had broken and was making and breaking contact with the bolt, hence the needle jumping around.
Soooo.....an electical circuit was constantly making and breaking, which must surely have resulted in a spark inside the tank!!??!? Near the top, above the level of the fuel, where there would have been air and petrol vapour. So how come it didn't just go bang? As the tank is right behind the back of the seat, I reckon I'd have noticed! So was I lucky or am I missing something?