I had a similar and strange problem which took me a while to figure out. My camera was working on the surface, but just stoped working during almost every one of my dives. I could not figure it out for the life of me. After loosing many great shots, I found that the foam inside the housing which keeps the camera aligned was compressed from extended use and the lever that pushed the shutter button was not in line with the button itself. Anyway, I shoved a quater in between the foam and the housing to push it out and now I am back in action. I never changed it either.

I don't know if that helped you, but I just wanted to share my brief story.