Depends on how bad it is....

If it's really bad, having loads of shit on it and going Blue and Yellow get at it with a wire cup brush on an angle grinder first.

Soak the thing in WD40 for about an hour then simply skim over it with the grinder to bring the true colour back then use wet'n dry sand paper 1800 grade with Autosol,

THEN use soft cloth to buff it.

Don't waste your money on autosol if it's bad to begin with, you'll use tubes of the stuff....