It's possible that it came from the valve cover when I re-shimmed. I wiped it all clean under the oil tank and it hasn't came back in about two hundred miles (it was only about a drop anyway). I already bought the o-rings and thought I'd throw them in just as a precaution until I found out you have to pull the TB's. That's not a problem, but I'm a lazy f__ck. I'll do it if and when it really needs it ! Thanks for replies. Fred