Yes this is a common problem with all seatbelt winders, once they have gotten to be a certain age.... It generally has to do with all the grime, and other build up the belts have been exposed to with heavy/longterm use... Our Trucks will have even more of a problem, even after a shorter time frame, due to the location of the retractor mech....
Usually one can get away with giving the belts a good detailed cleaning, and removing as much grime as possible from the Mechs themselves... Note when Cleaning the Belts, never use any harsh chemicals or bleaches, as they will weaken the belt meterial.... Always use only a nice Warm/Luke Warm water, to keep the belts from shrinking... Use only a Mild Preferable Non-Detergent type soap, and a soft but firm plastic/nylon bristle brush for subborn stains(Sometimes it is necessary to soak the belts, but make sure you do not submerge or expose the Retractor Mechs/Belt Buckles to water, as they will freeze up) ....