hmm...my 00 disco doesnt leak around the windshield, had problems with front carpets being wet, turned out to be the a/c tubes were clogged...im sure if you left the car in intense heat for long periods of time the plastic would warp, but I dont see it very likely...possible, but not likely...
as for the windshield thing, was yours a heated windshield? or just the regular one? I've got a couple small rock chips in mine and in the evening if the sun hits it right it looks terrible...debating on replacing it.
Diamondite® Glass Repair System Kit polishes out scratches in auto glass windshields and windows. Diamondite Glass polish restore car glass. Anyone tried that? supposed to be a resurfacing kit for glass...I've heard good things, never personally used one though.
When you said drain tubes were clear, were you referring to the ones on the sunroof or the ones to the A/C?