Maybe a bit late to contribute to this, but I've found isopropyl alcohol completely removes the matt paint they use on Lima coaches very easily, i was in fact only wanting to remove the lettering but it strips the paint before it touches the printed on 'decals' which needed some further rubbing to get them all off...I now have a very clean black plastic shell , ( it hasnt attacked the plastic btw)...as it happens its not too tragic as I was going to change the colour anyway!
I've got another wagon soaking overnight in Dot 4 brake fluid, the ipa wouldn't touch this one ( someone else's diy paint job, who knows what paint they used)