I could have sworn I've heard this eluded to somewhere but I can't find it, so before I tear into it, I wanted to ask, can the Walbro 255 be rebuilt? If so what parts are required? Just o-rings if it's functioning but letting the pressure drop too low?

My car's brief fuel history:
I bought it from somebody who didn't set it up well. She put a Walbro 255 in and a DSMLink V3, but she never turned on any of the settings for the FPR in DSMLink. I installed an AFPR, checked the pressure and found it was nearly 75 psi. I turned it down to 40 psi, tuned it, and found that my wideband was quickly increasing (diverging from the estimated AFR) under load and the boost was creeping. I retarded timing enough to tune out all the knock and still had AFR problems and hesitation. When I adjusted the AFPR as low as it would go, pressure dropped to about 20 psi, leading me to believe that I have a fuel pump that is no longer functioning well - hence my question.

Thanks ahead of time for the help!

Once a wally goes bad or debris gets into the pump and locks the rotors, ITS FINISHED. Some have gotten lucky and dislodged the junk that was jamming the rotors BUT it's a throw away deal once its done.

Make sure you don't have a leak inside the tank for the pump, did you set the base fuel pressure with the vac line off? Make sure you plug the vac line with something while your adjusting as well.

^ What he said. If this happens, just get a new one, their cheap enough, and can be had even cheaper in the classifieds.