Well, 2 lessons learnt. 1) Be more careful with microfibre cloths. 2) If heat got the mess there, heat will get it off. I ran the bike for a couple of minutes. Using a cotton rag soaked in WD40 I rubbed the hot pipe. The crap came off as a brown sticky mess (no, it didn't stink!). I repeated it once after the pipe cooled and the jobs a cracker. Cheers.