Tim, being that my cracks are black!, I used to get this all the time. Like scott said, I spray detailer onto a soft paint brush and that always does the trick  I now use Blackfire products which aren't as bad with dust.
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10 Years of Scoobies:04 WRX SL, 06 HAWK STI, 97 JDM WRX STI WAGON, 05 WRX STI, MK3 FOCUS RS, now Porsche Cayman S
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