DIY Slik Stik joystick for Atari, repair rubber washer spring?

I have 5 or 6 of these Slik Stik joysticks for Atari 2600/Commodore 64, but they all inevitably break, which is too bad because they have a nice feel.

The main problems are the self-centering "spring" is a rubber washer around the stick that deteriorates, or the metal shaft bends. The bent shaft is easy to fix (just bend it back into shape).

But could anyone suggest how to replace the rubber spring?  Preferably something that is
* cheap, quick, easy
* uses readily available parts
* won't degrade over time too much
* looks OK (not too noticeable a hack)

It would be nice to fix these so that they last, I just don't have the time / skills to get into a really complicated project.

I think there are parts online but if there is an easy cheaper DIY solution I would prefer that

Picture of DIY Slik Stik joystick for Atari, repair rubber washer spring?
I can't really tell what the washer looks like from the picture or any of the items shown at the link.

If it is just a rubber washer, you could try the plumbing department of a hardware store. If you have any rubber pieces around you could cut out your own. I can't get more specific than that, as I don't know the exact shape or the consistency of the rubber washer you need.