worked on the nose this winter. I sanded the cracks out, used spot putty, and primered it ($1.99/can at pep boys). still in primer i drove it this summer. bunch of cracks all came back on the nose. is it because the primer isn't strong enough and if it had paint it wouldve held, or is it because i didn't sand down far enough to get rid of the original crack?

 

you need a flex additive in the paint and primer and clear you are using to pain tyour urethane parts with

 

Badandy's got it right. You'll need a special kind of primer for flexable parts. You also do need to sand the paint down completely where it is cracked though, or it will continue to come back.