I'll share an easy way to get all of the oxidation out of fiberglass or metal. Oxidation is the usual cosmetic issue since it appears to be through the material surface.
Go to one of the big box stores or a paint seller and buy one gallon of Jasco Prepaint Conditioner. It is a TSP substitute. Spray it onto the surface to be cleaned (I use a one gallon garden sprayer). Let sit or brush surface for severe discoloration. Respray the surface and immediately rinse. If the Jasco drys, it needs to be rewetted with more Jasco as the oxidation will cling to the surface.
When dry, if the surface is matte flat, cover it with a good quality wax or you can even paint it with a gloss paint.
The procedure above is much easier than using a buffer and compounds and the results will be the same.