Wow! I've been reading here for years about cracked dashes, but I never realized how bad some were. So far, knock wood, my 96 dash is perfect. I credit the longevity to my "environmentally friendly" lack of ever cleaning it. :-laf
Seriously, after reading what interior cleaning/shining products can do to the plastic's chemical composition, I have never used any. I just wipe it down with a damp cloth once in a long while. I'm going to get a carpet dash mat to lay on it for sun protection. Then all I need do is shake the rug now and then.
Has anyone ever come up with a definitive answer on why so many dashes cracked so quickly and badly?