No, its a metal outer.
I have in the past cut a slit and twisted it over the ball (remove the spring behind the seal lip first, it will stretch over the ball) as a quick bodge.
Remember to put the slit to the top of the housing.
Clean them, soak with ATF/acetone mix for a few hours- much longer if possible with repeat soaking.
Tight fitting ring-spanner and tighten the bolt first, then try undoing.
Those that don't undo, cut off the heads.
It's worth whatever someone will pay for it.
If you're never going to sell it, then what it might be worth is immaterial.
Only another 16 posts to go.
P.S. the half eaten Mars bar offer still stands..........but only for the next hour.