I'd like to mention here that one of the advantages to maintaining boats every day is that I've accumulated not only a great deal of experience with the techniques involved in removing stains safely and relatively gently but along with that I've also accumulated a rather extensive assortment of chemical cleaners and stain specific removers (my dry-cleaner consults with me and vice verse). The secret is to experiment, in as non-conspicuous a location as you can, until you find the right chemical for the job and then use only as much as you need for as short a time as possible to get the job done. If you have a pretty good idea what caused the stain, consult your dry cleaner. If he won't help you, find another dry cleaner.
