I took my '12 WRX to the dealership to fix the P0451 issue the other day. After about 2 hours they asked if I would be able to bring my car back a week later for them to take measurements to see if my camshaft sensor needs shims added. They stated that this ws a "bulletin" for these cars but I havent seen anything anywhere about it. I was wondering if anyone else has encountered this same "issue"? I did notice that they replaced my gas cap and I no longer get the CEL for P0451.