What questions should I ask the mechanic to troubleshoot before continuing repair process? ABS warning had come on the day before a road trip home, but gone off again within a couple miles, so next morning I just got on the freeway to go home since no brake problems were apparent. Couple stops at rest stops and one fuel up--no brake problems. Coming off the 800 mile road trip, I pulled off fwy to pee and get fuel 20 miles from home. As I came to stop on offramp, and the brakes felt "grabby" and the ABS warning light comes on again. After fueling up, restarted car, ABS light still on, but now brakes had become spongy. Drove to a nearby brake repair shop instead of my usual VW repair shop. They said my rear calipers drivers side pad was gone, and recommended a master cylinder replacement, replace calipers, pads, and flush system. I approved it, as it made sense at the time. They did it and said still spongy. For no additional charges, they have replaced master cylinder twice (new parts), flushed multiple times as they troubleshot, and recently they replaced the booster with a new one...still didn't fix it. They said they would take out the new booster and return it, put on my old booster.....They isolated each brake line to check function and determined that the right front brake output from the ABS module was not working. They now suggest they buy a used ABS module from either a gas or diesel model, and they would install it for me for just the cost of the ABS module and a couple hours labor. Should I proceed, or ask specific questions first??