Crystal clear sealers will not do much if anything for UV protection. You need to use a transparent but slightly tinted stain. The tint will absorb the UV rays prolonging the wood from turning gray. Any of these
Deck Stains will work.
You should use a
deck cleaner and a
deck brightener your old wood. This will make the older wood look much better but it will not match the new wood. Close but not exactly.