I purchased my GF670 new. When it arrived the rangefinder was off. I have read that this is not unusual for this camera. I realigned it myself by driving to an overlook and using the vertical lines of a multistory hospital building located 4+ miles away on a line. Setting this to be infinity seemed to do the trick. My pictures are now all sharp. Although admittedly I have not performed a critical focus test. But so far there does not seem to be a need.
Before sending it off I would try selecting a target much further away than 12 meters, then calibrating to that as infinity. Then see how close the intermediate distances are to correct. I would also not expect absolute perfection from any camera. Normal stopping down should cover any minor discrepancies.