I gave them a call sweepleader. After 30 minutes of conversation, they are stumped. I fired over a myriad of photos of the unit and they are going to talk with the machine shop to see if they can possibly rebuild the unit.
The specific part number cross references to a dual piston master for some reason in their books, and this single 1 1/4 master is a ghost to them. But, they are looking to see what's possible. I'll report back with what they find/determine.
I found a replacement as well, but it's NOS, and Lord knows those seals are dry-rotted as heck by now, so even a NOS unit would be in the same boat.