I'll be checking out an Invacare oxygen machine this Saturday. It has something like 11,000 hours on it.

They make rebuild kits for my Harris 25 regulator. I think I might try and rebuild the fuel reg myself. It seems pretty straight forward.

The oxygen reg must be kept completely free for oil, grease, and debris. Anything in the presence of pure oxygen becomes a real fire hazard. So if I decide to rebuild the oxygen reg it will be done professionally.