This is just an example, I don't remember the actual names.
This is just two of the many images I found a long with a host of threads
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Top picture is of an M1 Garand receiver (read the upside down heel stamp) Cal .30 M1, etc. Since the serial is blurred, we can't tell if its one of the later 7 million range serial numbered, Australian made, cast commercial receivers. So, it's likely a forged USGI receiver, and not relevant to this topic. Even the forged Garand receivers sometimes cracked when firing rifle grenades before corrective measures were enacted.
And as someone else said, SA Inc. never used surplus receivers for the M1A. They've always been cast. And in all honesty, the cast receivers themselves have a pretty good record for durability in the 40-45 years M1As have been around.