Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

The white O-rings are a great idea, but if that doesn't work out, there is a nearly forgotten product you might want to consider as a Plan B. 

It's called PlastiDip and is used among other things to put a rubbery plastic coating onto pliers that just have bare metal handles.  You'll want the liquid version, not the spray.

It's available in various colors from Amazon:

And at Menards and Ace Hardware.

Paul