The backglass for my Centaur 2 was also spotted. Sealed it with a nice thick coat of cabot's clear, it really holds the artwork together great 
Does Cabot's work okay? Only heard of using Krylon. (That caveman glass in the pic "moults" every time I look at it!)
Yep Cabot's is the go. It's the same stuff as Markseal, dry's a little yellow so windows need to be masked off prior to application. This is all I use now.
