Brake help. Already?

Since you had some pressure before you bled it, maybe try this trick=
When I worked on Japanese cars for years and I replaced a master or wheel cyl., I would do this. - Fill the master to the top and open the bleeder about 2 turns. It will gravity bleed quite well, and a continuous flow will keep the bubbles moving down to the bleeder screw. Just keep your eye on the fluid level and not go dry. Keep it going for a few minutes. And you can see the bubbles out of the bleeder.
Then with a helper that can pump the lever slow and steady, put one finger over the end of the open bleeder to act as a one-way valve. Your helper can squeeze about once a second and you will control flow with some finger pressure. When he starts to feel a steady resistance then close the bleeder and pressure it and release a few times. It should be tight then. If not then the master is a fault.
Just be careful not to get the brake fluid in your eye. !!!

Take the bleeder all the way out and look for rust in the bore and clean it out with a small wire and brake cleaner. The brake fluid should dribble out when you have it out. Just keep the reservoir full.

If there is a layer of mud on the bottom of the master, clean it out with brake clean and see if you can inspect the very small hole. Also the larger hole supplies fluid to pump.They have to be clear.

The larger hole supplies fluid to the piston and the small one is called a compensation port to allow the fluid under pressure to release pressure when you let off the brake, or it will stay pressurized and the brakes will drag.
If you actually see metal you had better rebuild or replace the cylinder. There are only 4 or 5 parts and it should be easy to inspect. Release the circlip and the piston will slide out.

Take the lever off and pull the rubber boot out and you will see the small clip and pry it out to release the piston.

That photo looks pretty good actually. The large hole is visible and below that small metal shield is the compensation port=very small hole.

Put some WD40 on it and pry it gently with a small screwdriver on the edges. It may be old and cracked already.