My Brother had his FC40 get wet, This is what it is doing and will also tell you what I have replaced. It looks to lock on gps just fine, but once in the air it will not stay put. it will start to head forward and it is difficult to control. If I switch it to Atti I have much better luck, but it is as if the gps is messed up. All updates and calibrations have been done. I have exchanged the GPS, Compass, all Motors and ESC, also switched out the NAZA M V2 and it still does it ! the only parts left that have not been replaced are the 5.8G Receiver board which I can not find anywhere and the power board. I am hoping someone has some insight on what might be happening.