Not a big problem unless the cover also carries the centering rings.

This one is for one of the 8" RCA Personal Portables, virtually every one I've seen has had this problem, this one's not as bad as most but the rings won't stay on the cover, also the notches on the cover and rings aren't just for looks on these sets, they are there so you can use a screwdriver to adjust them after the chassis is put back together.
A person could get by without the notches if they had to but it no doubt made it a lot easier to adjust on an assembly line basis.

I'm thinking a cover could be built using flat plastic that could be bent into a circle, or maybe some Pipe that's the right diameter could be used.
The plastic would also have to be able to be glued securely and be heat resistant, PVC perhaps?

Maybe a Hobby Shop would have a selection of Plastic that might suit the need? or Home Depot.

Seems like that would be the ideal piece to reproduce on a 3D printer......

Either that, or a vitamin jar lid. I was thinking maybe some type of axle seal with the inner spring removed as well.

http://www.videokarma.org/showthread.php?t=203537 Eric, i think u will find what need here. Styrene is the answer.

Oops... i see you were part of that thread. My bad... sorry bout that.

Thanks Charlie, I remembered someone had rebuilt one but couldn't find it.

I was thinking of trying to find a couple sizes of PVC pipe, one for the large diameter and one for the small, then some flat stuff to connect them.

I have a mini lathe (not currently working) so I could turn them down to the exact sizes I need, the rings could be held on by gluing a small retaining sleeve on to the center post.
PVC is very easy to permanently glue and it's used for hot water so it should be temp resistant, might be difficultt o find the right stuff though.

There's a Hobby Shop in town, I could pop in and see what they have in the way of Styrene.

They make that liquid plastic stuff that you supposedly can dip a tool or something in and it will harden to give the tool a hand grip. I'd just buy a better tool myself, but anyway; if you could make a mold and pour that in it then you would have a duplicate.

That 3D printer is a good idea if you have a better reason than reproducing yoke covers for the investment. Amazing contraption really...