They can be re-webbed but 90% of the time rear belts will just need a good cleaning as mentioned above, especially the retractor side since webbing is protected inside the plastic housing; use 50/50 mixture of Down and water and a clean towel. You can clean the female portions in a dish washer as well, make sure wife is not around... When done, put a few drops of sewing machine oil on each side of the spool that holds the webbing inside the retractor. Re-webbing the retractor is a complex process, especially with old OE Autoflug and Repa retractors. I avoid doing that most of the time unless webbing is trashed, even made a few fellows angry when I refused to reweb the retractors since webbing was in like-new condition, needing only a good cleaning.
P.S. Australia used to make quality seat belts when Autoliv/Klippan had factories there before they pulled out of market, about 6 may be 8 years ago. I still have some of those NOS front and rear 3 point automatic Autoliv/Klippan sets if anybody is interested (these are the real ones, not US made versions manufactured by the seat-belt cartel🤬).