I cannot suggest something I haven't tried, but I will try it soon and tell yopu the results. I mentioned this method some other times in this forum, but so far I did not need to use it myself.
The item is caustic soda (was mainly used to unblock drain pipes too), when I was in model aircrafts, many of my friends used it to strip off bad paint jobs, and the plastic detail remained untouched, even though model aircrafts have very thin plastic shells.
I will try it sometime, when I start weathering / painting Locos, then I will tell you the result.