[steam for ever]

Painting can be a problem.
When painting something like a locomotive, it is probably best to get rid of the existing paint jobs first and not let them build up.
If this continues, the paint will flake off in big bits.
As far as I know this hasn't been done in the world of rail, but I did it on a sheet of metal using enamel paint like you would.
Just as advice, don't let is build up too far.