I use Rain-X on my vehicles and I like the job that it does especially in mist and light rain, but I've haven't noticed any help with the cracks and pits. Good Luck.

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1983 300D Silver -mine- 185,000 w/ donor transmission
1983 300D Gray (Franklin) -parts car- 180,000- no transmission and no oil pan
1994 S320 Silver -wife's-135,000