Posting a picture of the stain could be helpful along with the source of the stain, if known. Different stains can be treated differently. And was that L.A.'s Totally Awesome or Simple Green that you used. For the toughest of stains, L.A.'s Totally Awesome usually does a great job but has it's limitations.
I would be tempted to use lighter fluid (not charcoal starter fluid) as it is a mild petroleum distillate and safe on every plastic I've ever used it on. Failing that, try a light rubbing of acetone on a discrete area to see if it will dissolve the plastic before going after the affected area.
Indeed, painting with Krylon Fusion or other paint designed for plastic would be acceptable after a good surface prep/wash.
