Minolta XTSi Focusing Screen

Has anyone else experienced this problem? I had a Minolta XTSi, stored it in a hard case for a few years and later found the focusing screen had discoloured down the centre. It's a rainbow discolouration similar to the look of plastic through polarized lenses. I recently bought another XTSi kit (really just for the 75-300mm zoom) and noticed this XTSi has the same problem. This has never happened to any other camera I've owned, at any age. Any thoughts?

Nope, none of my Minoltas show this, but I do use them regular. Try to put the camera in UV light and maybe it goes away.

If it looks like a duck...

the focusing screen could in fact be plastic and thats why its looks the way it does, the Nikon FE2 or FE has a plastic screen and they warn about type of cleaners used on them