The thunderstorms locally have put paid to my plans to post a picture of this at the moment, but my oil leak is now hopefully fixed with a new sump plug and washer.
My local bike fixing chap gave me the old plug and washer as a souvenir, the oem equipment BMW alloy washer was corroding and likely the culprit. I'll be watching to see if the new stainless bits do the job.
Close up picture of old scabby corroded washer to follow in the gallery.