I remember recently there was another thread about a Lionmaster Big Boy with smoke unit issues that turned out to be from the AC regulator although Lionel no longer has an exactly matching replacement part. In your case however I'd start with some basic diagnostics, which I can't tell from the video: (1) can you hear the fan motor running/pulsing when the engine moves? (2) is there any heat coming out of the stack when the engine is on? (3) have you adjusted the smoke output in the CAB2 settings?
After that length of time on the shelf it's possible that the fan motor has been gummed up by smoke fluid residue. I have Legacy smoke units from roughly the same period that tend to need fan motor replacement after a long period of display/non-running. The motors probably weren't that reliable to begin with but without being run they can fail.
