Product Review: My main primer for the the plastic/urethane body parts is the SEM 39133 flexible primer/surfacer, made for automotive plastics. In an effort to reduce costs on the side covers, I tried the Transtar 4603 2in1 primer/sealer. I like how the Transtar seals, BUT it has it's faults. SEM adheres way better to the plastics and easier to sand. The Transtart has a difficult time adhering to the plastics. So out goes the Transtar and I am staying with the SEM primer as the SEM product is much more superior. Of course it's $10-$12 more a can(SEM cost $21-$24 per can), but it is well worth the money spent to have a quality item.