It won't go back in!!!!
I'm talking about my driver side seat belt . At first I thought the tensioner might be going bad, until I looked under the belt and saw loads of "gunk" on the belt holder. Took some Simple Green, gave it a spritz, let it set and BOOM!!! Seatbelt works brand new. In and out without any problems. Did this on the passenger side too. See below for pics.
Before:
After:
Before:
After: