Bleeding new disc brake issue

[64chevmn]

During the restoration of my 64 c10 project, I added a front disc brake conversion kit with a new brake booster and master cylinder. When I tried to bleed the brakes tonight, I had brake fluid leaking out of what I think is the relief valve on the end of the proportioning valve. There appears to be a small rod in the center of the nut that moves slightly in and out when I'm pumping the brakes and fluid is dripping from it. I've bled several new brake systems with a proportioning valve in the past and I never had any leaks like this??? Do I have a bad valve or do I have another problem? The below picture shows the nut on the end of the valve that is leaking.