Bruk, I was considering my gasket material for the top seal. The bottom I put some pretty dense felt into it, I figured that should stop most airflow, but obviously I could be wrong. 
You can't get the original material, or I'd try that.
I'm going to take a look at the smoke unit top and see if a resurface job might be called for.
This is a truly dumb design, I wonder what genius at Lionel came up with this idea! 
