After some more thought I think I know what's happening:
I replaced the chain with one that has fatter links. The link I hang on requires me to rotate the chain 90 degrees to hang it, it doesn't line straight up to the hook. So the fatter links are binding on themselves as I go down the road causing some wear. (the wear is on the inside of the links where one link contacts the next)
So I'm going to replace the chain with one that more closely matches the original. Does anybody know what that could be? 30 grade 3/8"? 70 grade?
Thanks for all the replies
Scott