Aftermarket passenger car diaphragms for LIONEL?

I have a set of the LIONEL Aluminum Chesapeake and Ohio passenger cars - but they skimped on the rubber diaphragms on these otherwise nice cars.

Anything that will work? - because I can tell that gap is going to start bugging me eventually.

Used diaphragms are salty on ebay - would cost as much as the car to outfit each.

Thanks!