I know this thread is a bit old, but for those who bought an Aimpoint CompM2, you CAN send them in for repair.
The sight must have fogged from day 1 after I got it from law-guns, but I didn't take it outside for a few weeks, which is when it would actually fog... so I couldn't return it to law-guns any longer (they gave us 3 days to inspect).
After discovering this, I asked Aimpoint if I could send it in. I gave them the serial number with no mention of how I got it. They told me no problem send it right in. 7 weeks later I got it back. It was fixed without charge, they replaced the rear lens and rear tube.
Just FYI for those who discovered problems with their sights and weren't able to exchange them within the 3 day period.