74 Dart Seatbelts, how do they work correctly?

I had a rear belt retractor problem in my 73. When I removed it I couldn't see anything really wrong with it. I used compressed air to remove a small amount of dust / dirt collected in it and that cured it.
After thinking about it, I realized it did start acting up right ater we drove that car on vacation to the beach. Sandy children LOL
It dont take much debris to cause a problem in those mecanisms.