[3tas4me]

My 1974 Trans Am is almost finished, but we are running into a problem with the black section of the front bumper. The car has only 49k original miles and has been stored inside almost it's entire existence, hence, the bumpers appeared to be in very good condition. Some minor cracks were filled by V'ing them out and then using a flexible primer. The problem we are running into is that the bumper keeps getting cracks if it is flexed.

Is there a way to prevent this from happening again? This will be the third time repairing this bumper. I want to make sure we do it right. What is the shop doing wrong?