Vigo, I thought the same thing - but new Bosch pump, new 5/16" Stainless lines (with no kinks), new fuel filter and an original fpr make me think that's it. Besides, for $20 delivered, it's good insurance. I'm wondering if the boost pressure is deforming the diaphragm causing it to lose it's pressure on the relief valve......
I figured running with the return pinched off would run way rich off boost and I didn't want to clog the Cat.