The Falcon from which this wheel cylinder was pulled changed status from daily driver to hobby car in the mid 1980s. Since then it has gone through normal old car stuff such as floor replacement, several engine swaps, etc. It is likely the rear wheel cylinders corroded at least 20 years ago during those “back of the shop” years. Never had a problem going through PA inspections. After all the break linings always looked good. It is not like they ever made contact with the break drums. Sure breaking took a bit of muscle. I just assumed it was due to swapping a v6 for a v8 and keeping the v6 front drums all around with manual breaking. I also assumed the parking break was not working due to the cable being stretched and in need of adjustment. I was wrong on both counts.
State safety inspectors do not pull the dust cover from the wheel cylinders. Even this one looked fine with the dust cover in place. It is up to you to check under the covers. You will sleep better.