Thanks fella's
I've just got back in, but I'd already resorted to the self-tappers method mentioned by Matt - the seal came out no problem. My semi-local bike spares shop had the right size seal in stock so I'll slip it in tomorrow and hopefully that's another in the pretty long list of jobs sorted.
The kindly Racer38 has offered me a 3-way joint on loan so I'll hopefully get the poerjets hooked up as they should be tomorrow too and then I can try to figure out what's up with the carburation/intake that's causing the erratic idle and generally pretty poor running.
Cheers
Wb