From searching, this seems to be quite a common thing.
I've disassembled the watch and found that indeed the fogginess is between the crystal and the solar panel.
I've read some conflicting reports about whether I can press the glass out or not.
I'm also struggling to find either as spare parts, I don't mind giving it a crack at pushing the glass out, but I'd rather have a foggy mudman, than a broken mudman.
So if I'm going to break it in the attempt, I'd feel much more comfortable if the parts are available.