Any supplier that sells automotive paint should have the flex agent as well. If you tell them what you are using the paint for, they should point you to the product you require. It comes in its own can and has to be mixed in with the paint just prior to application. Follow instructions as to mixing ratios to get the best results.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car