Its new. I even swapped another out to make sure it wasn't a manufacture flaw.
I picked this car up with a leaking brake hose. I replaced all the hoses, brakes dragged, I replaced a couple of calipers, still dragged.
Further trouble shooting (which is what I should have done originally) revealed the brakes would release if I pull the master cylinder from the booster rod creating freeplay.
I measured the portion of the rod sticking beyond the booster housing to be about 3mm more than another 123. This car is an '80, the other was an '83. I don't know if there's a difference or not.
I temp solved the problem by drilling the master cylinder's piston 3mm. I was concerned about "punch thru" of the piston so I made several very hard stops. Seemed to work ok.
Now I get back to this project and find they are dragging slightly again.
Stumped.