Connetts,
Erudite and informative, and a very good post.
However, this, and all the other sideways discussions tend to take away from the fundamental point.
Any contamination on any surface means no go.
This really is black and white and I can't believe some of the posts on this thread.
Some real insanity here. Right from my very first PPL flight, it was a given. If there is anything other than paint on the wings, it needs to be removed. Full. Bloody. Stop.