If it really sat 9 months, they might be too far gone. Sun and weather is really hard, even for marine vinyl. You could try a spray bottle of bleach and water and see if it would help, but I'm betting they need to be recovered.
Have you tried powerwashing them?
Capt. Craig Copeland
2013 Nautic Star 2110 Shallow Bay Boat
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)