WD-40 does wonders to anything plastic. I used to use it, now I just use window cleaner and a clean rag, but I clean my engine bay everytime I change my oil so it never gets very dirty. Engine degreaser, scrub, rinse and coat it with WD-40 (i would rinse again to remove the extra WD-40) and let the engine run and dry itself off.

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Touring the nation, one state at a time