seat belts - '63 Riviera - chrome split-top

I'm lookng for black replacement Buick belts for a '63 Riviera. They are the chrome split-top with the Buick logo on them. See Pic

The retractors work fine and the belts latch fine and hold as they should, but I can no longer adjust the length (unless I remove the cover with a screw driver) Is there an easy fix to this?

Must I send them out to be replaced? If so, any recommnedations or expected price I should pay for these replacements?

Thanks

 

anyone?

So no one has ever tried to refurbish their own seat belts?

 

I found an ad in the ROA (Riviera Owners Association) Riview but it came from Hemmings Motor News. Goodluck :TU:

"Seat belts restored to show quality SsnakeOly Products, Inc., 114 N. Glenwood Blvd., Tyler TX 75702, (800) 284-7777, FAX: (903) 769-4552"