2 destroyed starters in a row...WTH?

I had exactly the same problem and broke two noses off of the mini starters. My issue was while cranking the distributor vac advance started advancing. Yes it was on the ported vacuum port. Weird as heck to find. Use your timing light while cranking and see if it is advancing while cranking. I made a full mechanical distributor and have not had a issue since. Hope it helps.