My GZ pump has required no maintenance. The motor runs .9mm stainless rings. This is the 2nd time with these style rings. They were fine before it spun a bearing breaking a rod. Currently is coming up on 200 runs. Both times there has been no degrade in performance, oil usage, smoke, or blow by that I can tell. What are they worth performance wise? Hard to tell Its always had a vaccum pump, 10-12 in/hg. all things being the same I'd say maybe .05-.10 for the rings over the .043" that were there originally. Though the .043" ran pretty well. It has alway been honed with a plate. I should add it has verticlal gas ports as well.
Doug