I repaired a broken one Iamichabod gave me. As CloudDriver points out, if the area that broke held the clip that retains a very stiff coil spring, it was assembled by Velvac using a hydraulic press.
I thought a bolt or threaded rod could accomplish that pressing action, and did a quick cut at a repair using a 1/2" bolt with nut up inside the piece that mounts to the coach body.
That won't allow wiring, but I think I found that 3/8" threaded tubing, like used in lamps and light fixtures, would fit and still do the job. Don't hold me to 3/8", might have been 1/4" but I think 3/8 is right. Fit very close to the approx 5/8" inner bore of the piece the clip breaks out, so could be set with epoxy.
Would probably require cutting and splicing any wiring, because a connector likely would not slip through the tubing's smaller diameter.
This shows the broken retaining ridge of the pot metal pivot the arm swings on
You can see the only remaining ridge is from about 2:00 to 4:00 clock position on the edge of the pivot. You can also see the 1/2" nut I tapped into the top of the hole to accept the bolt in the next pic. To actually finalize this, I would want to go back and remove all of the remaining ridge. That would cause clamping to be straighter, and down closer to the original parts spacing.
Here it is with the bolt in place and arm secured. If it was mine, and I had no wiring to re-install, I would put it back in service and call it Good, even though the plastic trim cap wouldn't fit.
I believe that with tubing epoxied in place, the Thin Nuts available for lighting fixtures, and leaving a "tail" to start compressing the Spring with, wiring could pass through and the Cap could go back on. The "tail" would be cut off flush to the Nut once the assembly was pulled back together. RED LocTite on the Nut Threads!
Unintended Consequence Warning: I rate this fix as Better than New, because the connection is now Steel and not Pot Metal. So, if a child decides to do chin-ups on your mirror arm, that Velvac isn't gonna break. It'll spring the mounting area on the cab door.