More troubles with new master cylinder

Know this... If you go under the dash, separate the rod from the pedal and pull that rod hard enough... you might pull the master cylinder apart ( this was seen in a recent thread too ). In most cases there's nothing more than a sheet metal finger/keeper holding the spool valve in the master cylinder. Combine significant pull with the internal return spring already applying some pressure against that finger/keeper. So anyway IF the rod with rubber ring was fully seated at the workbench, or even kicked in with the pedal, it's not likely the problem and pulling there can become a different larger problem. Good luck with it