The best glue for these plastics is, still, plastic cement. That's what they are for. Plastic cement is actually a solvent, so the parts become one. Any decent brand will do. I use Testors; keeps forever, too. You can buy a boutique brand if you like, but it's all plastic cement.
The paint would probably not be a problem for the bond, but if you can scrape it off with a sharp knife without damaging other areas, it couldn't hurt.
(The best cure for this problem is the use of metal steps; MTH used to do this a lot. The reason I quit buying Atlas rolling stock was the plastic steps, many of which still decorate my right-of-way. But, I think most use the plastic, now. D**n silly practice. How much more could the metal steps and installation increase the cost....on an expensive model...?)
