Big Problems with New 408 +PICS

If I had to guess, I would say the rings in that hole butted and wore the block away. Did you get a sheet with the measurements for the ring gaps? Look a the ends of the rings (where they were filed in the gap) and see if there are any marks that looks like they hit and rubbed on each other. The good holes should show no signs of contact, that one should be pretty obvious. Shiney spots are what you'd see, as opposed to the gritty marks the grinder leaves. Another way to check is put the work rings in the bore and measure the end gap. With the hole .005-.008 larger bore, those gaps should be like .035-.040. If it's tighter than that, they were probably much too tight when fresh.