Unfortunately, it's much more than a mere loose screw. You will need a new seat rail assembly. Had mine fixed by my dealer. The good news is that it's covered by your warranty. The bad news is that it may be difficult for them to find the parts.
When I first complained to my dealer, the response was, "This is normal." To which I responded, "
! Fix it!
" It took them a couple of days to find the parts. The first replacement rails were as bad as the originals, but the second set were just fine.