Right, I've taken off the airfilter box and had a look down.
It looks to me like oil leaking from the condenser - there is no oil anywhere else locally to the condenser. If it was engine oil or gearbox oil it would have to be sprayed onto it and it would make mess all over the place.
My question now is, how serious is it? Should I get it looked at straight away?
There seems to be a bolt on top of the condenser which I haven't tightened up but looks bit suspect.
Cheers for the posts so far.