Quick question, is this what the trolley does? Just for clarification. Skip to 1:51 in the video
https://m.youtube.com/watch?v=3sG7KSLYkgM
If so, the guy that made this video put a new “top board” in the locomotive and it worked fine as it appeared.
https://m.youtube.com/watch?v=W2tXFt1Ew6Q