Thanks for the swift reply, and sorry I've taken so long to get back to you. I've just got back from a few days of bombing around France!!
It seems that my cylinders are ok, at least so far...
As for the air filter issue, I'm still getting petrol coming back into the air box (has anyone noticed how the petrol in France smells different to British fuel?). Unfortunately I haven't had a chance to do anything about it, but I'm fairly sure that the oil level has been fine all along. I'm going to have a look at it tomorrow when I price up some bits for a little freshen up (new chain and sprockets). Just a thought though, if the petcock was malfunctioning, would the fuel tank not leak when I take it off? I haven't had a problem with that at all. Also, any idea how hard and/or time-consuming it is to take off the carbs, and do I need anything special such as a vacuum gauge?
Thanks!