Brake fluid is what I use. Hasn't harmed even the RT era guard plastics.
Strips enamel paint OR acrylic paint (you may have to scrub with an old toothbrush - but wear gloves as it will seep into your skin and leach the fat from it). Potent, but can't be just poured down the sink afterwards, needs specialist disposal).
Simple Green is what I believe Lav25 Gunner was referring to. It's a biodegradable cleaning solvent. Is supposed to work, but my local hardware doesn't stock it and the nearest "big" one doesn't either.