I've got a bit of metal with plastic bits attached (wind deflector for a car
sunroof). There's no obvious way to remove the plastic bits, and I don't
want to break them, as it'll mean a new part.

If I use a paint stripper like nitromors, am I likely to dissolve the
plastic? It's a fairly complicated shape but I could most likely remove a
fair bit of paint and surface rust with a dremel. I intend to paint it with
hammerite, but these things tend to spend a lot of time in water / damp.