Yesterday I had to make it over the Coquihalla pass and got blindsided by a snowstorm on the West side of the pass. Long story short I switched the wipers from low to high because it was getting pretty bad and the passenger side swung into the drivers wiper and they jammed. Ended up having to get towed into town to make a temporary fix by tying back the freehanging linkage.
I was able to get into it today and found that nothing is broken, just the arm popped off a plastic hub on the pivot and bushing assembly. Popped right back in and worked fine.
(https://i11.photobucket.com/albums/a166/ballsandy/New%20Bucket/IMG_0936s.jpg)
The microfiche in the Eaglepedia (http://amceaglesden.com/guide/85.XX_Wiper_Assembly) doesn't state this is a replaceable part (and doesn't even show it) and it wobbles around quite a bit once assembled with LOTS of play. I can't tell if this is normal and it's a safety release or it's heavily worn.
You are correct; its not a "serviceable" part. If you want to try to find a tighter version, any later-model AMC small car with electric wipers will fit (Hornet, Gremlin, Concord, Spirit, Eagle). I see them on Ebay a lot.
Okay well that confirms what I predicted and there's replacements available if need be. For now I've popped it all back together and so far it has behaved so we'll see how it handles.
I've replaced mine