Many thanks for all the input. I tried the Pine Sol method with an old Weaver box car and it worked perfectly. Not so with a K line and a Lionel passenger car - perhaps because I didn't wait long enough for the soak, but six hours seemed enough time and I was worried about weakening the plastic.
So, I picked up the ESO and have completed two cars by hand. The original paint has been removed with ESO and the plastic does not appear to have suffered.