[Eddie Z]

Thank you for your suggestion - now I'm worried that the hub indeed may have expanded so much that the dial and mask were both stuck to it, as well as the spacer.  That might explain why both the dial and the mask had a crack started from the hub, and when I gently pried the dial off, it cracked the rest of the way up.  If might also explain why the mask "pops" slightly back and forth if you flex it forward and backward - all suggestive that the hub is wider than it is supposed to be.  

I have tried heating the spacer at 12 points around its circumference, first with 20W, then with a 200W Weller gun applied for 15 seconds per point until it was pretty warm - but not at all hot enough to damage the mask, then buzzing it stoutly with a "Multitool" through a firm stick of wood, and it still did not loosen at all.  After that, I applied a few drops of Superlube Syncopen "synthetic penetrating oil" (hoping that kind would be the least threatening to the mask), then buzzing it again afterward, and again 12 hours later, and again tonight - with no effect at all - except I'm convinced that the inside of the spacer must be fully coated with the pen-oil now because the mask now has a slight but obvious "oily" look to it for about 1/2" to 1" away from the hub - so the pen-oil must have made it all the way through the spacer, all the way around - and buzzing it again still has no effect - it's just stuck hard and won't come off.  

Anyone see any way of saving the situation without hurting the phenolic mask?  Thanks, Eddie Z.