I hear ya on this... mine have a considerable wear/flat spot on the rings. I've got some replacement parts, but I don't recall having those rings.I had one back in the 70's and it was great, but it's got one bad design flaw. The spring attaches to pin on the outside half of the stroke adjustment. This can wear.. and will eventually break. I think this pedal would rule with an infinite stroke adjust and better spring attachment. It was way ahead of it's time.
I would like to see a ball bearing feature there like Pearl or Tama have on their spring. I also had mixed feelings how that spring connected on the other end of that tensioner... it could use some design attention too.