I'm the same way--isopropyl is my go-to, and I have both the 71% and 90% depending on the paint. It's exactly like you said; some stuff comes right off, others you need to work at. Only mentioned the clear-plastic thing as I've come across it a couple of times. I won't say 90% causes that every time on clear plastics, but I think it's safer to use something else in that case. And I'd heard of oven cleaner but never used it. I also remember Brasso was a good one for plastics, and I used to use it when I was customizing Alternators way back when.