managed to clean up mine with a 5 minute (cut)simple green soak, a hotsy pressure wash (local car wash, hot water), and vitamin e oil (70,000 iu from cvs $10, its clear. paint on, let sit wipe off till dry.) they were the same color as yours when i started. (the one in back is pressure washed and dried, the one in front has e oil on it soaking, pre-wipe off.
39 years of funk and sun dried goodness in before.
5 min simple green soak and 15 min hot pressure wash in after.
Anyone know of a nylon composite sealant?