Ixixly, "badly frayed" may be too much. Chafing and fading of seatbelts are sufficient to require replacement.
AWB 25-2 Issue 1, 4 April 2003 includes this description...
Recommendation
Remove from service and destroy all seat belts and shoulder harness webbing when it reaches 10 years time in service.
Implement inspection procedures to ensure that safety belts and shoulder harness assemblies, particularly those in the pilot and co-pilot positions, are maintained during the recommended ten-year service life to a standard that requires prematurely faded, chafed, or otherwise damaged or chemically contaminated seat belt webbing to be replaced with serviceable assemblies.