Hey Doug,
Not an expert by any stretch of the imagination and only guess at some things. I have used brake fluid, in the past, that attacked the plastic and made it very brittle. I have just recently used 91% isopropyl on a ConCor box car that was a blue color and also on an auxiliary tender that was Daylight colors. After soaking for a couple of hours an old stiff tooth brush removed most of the paint. The orange and red on the tender is being a little stubborn, maybe because it is TruColor brand ? ? ? BTW the plastic has not been attacked.
Carl