17/16 Z32 Tokico MC small 4th port question

[turtl631]

I'm running a Napa remanufactured Z32 17/16 Tokico MC. I removed the annoying 5 sided plug, pressed in the flare fitting from the stock MC, and got the MC installed. After bleeding the system completely my buddy noticed that some fluid was dripping off the MC when I pushed on the brake pedal. It turns out that this MC has a small port in between the 2 front brake line ports and the 1 rear brake line port. It was originally plugged with a small rubber piece, but that has since popped out. The inside is not threaded, and it has a tiny hole at the end that brake fluid dribbles out of when you push hard on the brake pedal.
What is this port?
How can I plug it?

[turtl631]

Never mind, I'm gonna return or sell this thing. Not worth the hassle for me to try to plug the hole reliably. Nabco 17/16, here I come.