Grit (as in little stones) is OK apart from when it chips your paint.... it's the grit (chunks of salt) off the council's wagons that is the problem. Left to its own devices salt will corrode anything it touches on a car, it's just the amount of time it's left that makes the difference. Obviously some parts are more vulnerable than others, but clean it off pronto and you should be fine.
As far as I'm aware wax will help protect your paintwork but you'll still need to clean that salty residue off. No idea if there should be any problem as far as sealants go. Tbh I reckon with regular checking and cleaning you'd have no problems.