I don't have a dog in this fight regarding the Rockwell model T, but I'm a bit curious about Zamak. I have quite a few pre-WWII German slants and some are all Zamak, and others the plated heads are. I had always thought that Merkur had brass heads and only recently read that they are Zamak. I don't have any 'deteriorated' Zamak on any of these razors, and I probably have close to 50 of them.
It certainly disappointed me to find out that the Merkurs are partially made out of what is essentially referred to as 'pot metal', but the 137 was the best slant I ever cut a whisker with until the Wunderbar came down the pike. All I'm saying is, though brass would be more desirable, the Zamak isn't 'that' bad. IMHO.