If you have gotten this rust protection spray for the under body like a few yrs ago is it possible tog et it again? do they have to scrape off the old stuff? or just stick on a new coat? thanks. 6in 87' K5 w/ 35" BFG muds. Kn filter What I need: 4.11 gears, Lim Slip Dif, Force2 Catback, rear springs , Throtle body spacer.