I've heard of drilling a small hole at the end of the crack. This supposedly gives it a radius and prevents it from going further. I haven't tried it myself. But really there is not much you can do except to park in the shade to slow down any further damage.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma