[DylanVK]

Good info already here... I'll add my little side note:

DO IT RIGHT OR DO IT TWICE!

Theres tons of things on the market that claim quick and easy fixes to faded lens problems. Usually they're full of oils and things that make it look better for a short time.

Removing the oxidized material - with cutting polishes (or sandpaper when needed) and then restoring protection might take more time, but it ensures you won't be fixing it again in a few weeks.