1) Clean the seat belt. No need to remove it from the car. Pull out the seat as far as it will go, attach a spring clamp to prevent it from retracting, dunk the belt in a small bucket of warm soapy water (I used Dawn dish soap) and swish it around, rinse and let dry. This makes the belt much more supple and able to move through the loop and retractor. I was pleasantly surprised to see all of the dirt and funk that was released from the belt when I did this.
For me, this helped a lot, but it did not cure my seatbelt retract woes.
2). Next on my To Do List is to tighten the rewind spring. See this YouTube video as it gives good advice:
Good luck. Let us know how it goes for you.