I didn't want to paint my gas tank on my MTD 990 because I believe it would eventually come off. It had discolored to a point of looking gray. I remember how rubbing some plastics with transmission fluid would give them an Armour All effect. I scrubbed it with soap & hot water & air hosed it dry. I gave it a couple of coats & rubbed it all in once a day for a few days & wiped the excess off. Here are the before & after three weeks later.