Oh yeah the coatings are tough alright. When Houghy gave me the EP he said "Clean this with whatever you like..." if I can get the surface clear, it's a step in the right direction.
You could be right, David. It may be a film on top of the coating. Still it's a tough film!
There must be some nasty stuff in insect repellents (and I suspect sunscreens) though. A mate of mine used Rid, and still had some on his hands when he picked up his camera. It started to dissolve the the plastic in his camera. It only affected the surface, but his camera has an ugly looking handprint permanently in the surface now.
Finger print ID of ownership!
...and people happily put this stuff on their skin.
Just shows how tough our skin is!
Al.