Thanks for the detailed reply Norman!
I haven't done the first tank of fuel yet but I note that the leakage rate has really dropped off, so it could have been a combination of clutch arm grease and chain oil as you suggested... just seemed too fluid though. Anyway, there's still a little oily fluid leaking, but it's hardly excessive, so could be from one of the fuel leakages you spoke of. I'll keep an eye out.
I'm convinced now that the noise is clutch/drive related. I had the clutch cover off and noticed when rocking the bike and forward a little, that the metallic noise was quiter (obviously, since no engine power) but clearer. Greasing up the drive gear and clutch wheel made no difference to the noise. (I couldn't believe those gears came unlubed!!! What the?!?!) I've seen a few more "you tube" vids that have exactly the same noise in them, so it's apparently normal... I might end up employing one of the clutch cover ideas I've seen in here.
I also checked the spark plug and it's fine - so it's not a piston smashing into the plug kinda noise.
By the way, I've lubed the chain with transmission fluid - anyone violently reacting to that idea?
Cheers all and thanks for the responses.
Rob