The story that I have heard is that the conditioners used in the formula will dry out and crack the vinyl unless you continue to re-apply Armour all to add moisture.
I used to use it all the time, hence I had no problem as I was always moisturizing the vinyl. I have switched to STP Son of a Gun and I find it a much better product. One application a year keeps the dash looking shiny and new!
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Driving: 1998 F-150
Far way in Edmonton==>
1995 Mustang GT