The first two housings I had were OEM housings that was the reason for the change to anything but factory. Then when I got the Dorman housing I found out that the housing was a factory housing with a worthless pre-installed thermostat (that didn't work) and what looked to be a little thicker slice of inner tube seal. But Dorman didn't mold the housing I got, just repackaged an OEM.
Which brings me to a suggestion for others here, if you end up with a Dorman housing I for sure wouldn't leave there cheap thermostat in it! the one in mine never OPENED the first time!