All back together and working perfectly.... though I'm hoping I haven't jinxed myself.. Just in case any other mechanical newbies are wondering whether to have a go at this I'll give you my experience. Working very slowly, in cramped conditions, this took me about 6 hours. I've a fairly decent toolkit but actually, only a couple of sockets and allan keys needed. I drained the oil and put the bike on an Abba stand which made it easier. If you had a motorcycle lift or table it would help a lot more. Definitely order a new gasket. My dealer took a few days to get one and it probably is wise to use a new one. Take lots of pictures and refer to them! Thanks again to all those who chipped in with advice and PM's when my knowledge ran out! This is a great forum where people are immensely patient and generous with their time.
Nice one! Pretty sure you don’t need to drain the oil. At least I don’t think I did when I did mine .
I followed the instructions from Stu675 which were really helpful and in a how to on here. Essentially, I disconnected the CPS plug which runs from the stator up under the petrol tank and measured the resistance between the two pins. It's supposed to be about 200-230 ohms (ish). Mine showed infinite resistance. Ideally read his explanation though as it's much more technical and thorough than mine. It's the white plug in the below picture.