There certainly can be a world of difference...... "Red rust primer" is an imprecise description but it conjures up visions of $6 a gallon red oxide shop primer which tends to be worth every penny of the price. I would say get more info on exactly what it is and assume it's going to cause you more trouble than it's worth. You probably won't want to put your epoxy and the rest of the automotive system over it because of compatability issues we've discussed before. Certainly the easy way out though....... for them!
Bruce Palmer
Salem OR
