Replacing the seat belt isn't that hard a job.
You don't need to remove the seat, just slide it all the way forward. The only tools needed are a 17mm and a phillips head screwdriver. You don't just replace the belt but rather the entire belt retractor mechanism. There is a small explosive charge that deploys in a level one crash which retracts the belt to keep you from peeling out the belt under the force of the crash.
To replace, after sliding the seat forward slip the plastic thing off the belt where it bolts to the floor then remove the 17mm bolt that holds it there. Next remove the two phillips head screws from the foot of the "B" pillar then pull down on the trim. The trim will unlatch from the pillar and you can slip it off the loose end of the belt.
Now remove the 17mm bolt that retains the belt at the adjustment mechanism. At the bottom of the "B" pillar there is one last 17mm bolt that holds the entire mechanism in. Remove that bolt and carefully pry off the electrical connector at the end of the squib (explosive charge). Now come the hard part.
Lift the entire mechanism upward into the pillar and tilt out to remove the whole assembly from the pillar. This might take a few tries, but can be done. There are two types of retractors, one has a turbine and the other has a piston - the piston type is harder to remove ('86 and later I think).
Assembly is the reverse of above. Note, when you plug the connector to the squib you MUST hear an audible click for the system to work.
I believe FastLane or PartsShop might have the assemblies for about $390.00 apiece.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.