Wait wait... a claybar is sort of like suggesting he take a .44 magnum squirrel hunting... use it wrong and it can make things WORSE. That may be an option down the road (and annual or semi-annual clay barring seems to be a good idea in general), but I'd think something a bit less drastic might be tried first I think, since we don't know what the deposits are.
Have you tried a mild polish like the McGuire's first? It used to be called Mirror Glaze but might have a different name now- it comes in VERY fine grades and has a very subtle grit in it, and that might give you a bit of grip on whatever it is. Sinceyou seemed to suggest above that it was on your glass and trim as well, I'd think it is mineral stains or something from your water. Are you washing in the sun, where the water is insta-dried on the paint?
If you try Macguire's, test it on a stain somewhere not noticable (or at least LESS noticable) first and save the bonnet and such until you're sure it will help. The Mirror Glaze is great stuff though- we used to use it at a motorcycle dealership to buff out scratches in TRANSPARENT plastic, that's how fine the "grit" in it is.
