In the past, I have had great results from products based on Citrus.
Oranges, lemons etc.
Not only is it safe and works really well, it smells lovely!
I'm gonna give my regular warning that gets trotted out whenever anybody suggests using Limonene based products on plastics. Limonene, the active ingredient in all the 'citrus' cleaners, is
not safe on plastics, contrary to popular belief. It
will dissolve most thermoplastics, it's just slower in action than other solvents that people have learned to be wary of such as organochlorides, aldehydes, esters and ketones. If it doesn't actually dissolve the plastics it will most likely cause hazing or solvent crazing.
It can be used
cautiously on plastic surfaces without causing
major harm
if it is used in a water/detergent/limonene emulsion. The usual applies, try it first on a bit of scrap or an inconspicious, non-functional part first. Don't use on stressed parts, solvent crazing can be invisible to the naked eye and can seriously reduce the strength of plastics parts.
I was using some Limonene to degrease some motor parts and didn't notice that I had spilled some. So the corner of the ABS case of my mini socket set sat stewing it it for a hour or so. When I picked it up, the outer layer had turning into a puddle of liquid and a long gooey mess of sticky filaments trailed back to it.
Here's the result after I scratched of the majority of the gooey bits and left the dissolved edges to self level and dry.

(Sorry about the crappy photo, but the forum's playing up and doesn't like the cropped, rotated, colour corrected version)
You can see where an approximately 3mm thick layer of ABS was dissolved through and sloughed off.