When it's bare like that, it should turn pretty easy, IMO. Not spin freely (like a bearing), but easy to turn with your hands. My feeling is that oil is apt to trap dirt and get sticky, so my preference is a dry lubricant, like Dry Moly
https://www.crcindustries.com/products/dry-moly-lube-11-wt-oz-03084.html
It comes out wet, but dries very quickly to leave just a slippery dry film. One of the dry "PTFE" lubes might work too, haven't tried them.
I've never had any luck repairing things like that with JB Weld. In spite of the hype, it's actually quite soft/weak, more so than even most plastics, let alone any kind of metal. Where it shines is either mating two close fitting items together (so there's lots of surface area to bond) or in combination with a high strength filler like fiberglass cloth/mat. Maybe I'm doing something wrong.
But, I don't know what else to suggest, other than sourcing used parts from another head. Although someone must make them, I don't know of anyone selling new individual pieces. Check with Marv Gruber or one of the other folks on here selling old parts.
Might be worth trying some of that "aluminum welding rod" (which is actually a solder I believe). I'm not sure what the ring is made of, the solder may not stick or the ring may melt before the solder does. But if you're going to throw it away anyway ...