I attached a link to a thread I had put together with photos of a new manufactured unit.
It is chinese made and there are certain things to keep an eye out for. I tore mine right down because the brake line fittings installed into the end cap were threaded to accept metric threads. The old fittings I had would not swap over to the new end cap as the end cap was also threaded differently. I ended up using my old end plate, then re-used my brake lines as they were with out a bunch of adapters.
When I had the new chinese built unit open; I found the main rod/shaft that is bolted to the large power piston had more play than I would have liked. So I also swapped all of the rubber sealing components onto the old power piston/rod assambly and set the new power piston/rod off to the side.
A lot of the internal components in the new units are made of plastic of some kind as compared to metal in the old unit. There are also differences in the compression springs used in the new unit.
I ended up building one very good unit out of both the new and the old units.