I just scrolled through ALL the Combat Master pics on Bing and think the mystery may be solved. Very few pictures show this area.
Given this bit of metal is thinner due to the slide scallop, I'm thinking they were prone to failure in that spot.
I found a sale ad on Guns International and that gun had a piece broken out in that spot. No, they're not the same gun but the serial numbers are only about 2K units apart.
