Yet another Combo/Proportioning Valve Question

Here's my current setup:
1953 Buick 2 door, stock V-8 with original drum brakes for the rear.
the front was chopped and a 1970 Chevy nova front was put on and now I've got discs on the front. ALL NEW lines, shoes and drums at the rear, calipers and rotors on the front, dual master cylinder and this proportioning valve:

http://www.speedwaymotors.com/GM-Disc-Drum-Proportioning-Valve-for-3-8-24-Outlets,46424.html

I bled the system starting from the furthest from the master cylinder.
No leaks except at what I think is called the metering valve. There's a sort of boot that installs over it. Do I remove this when bleeding? it's a very slow leak, but a leak none-the-less. I read something about resetting the meter valve rod?

I know very little about brakes and much less about this proportioning/metering/combo stuff. I've been reading some posts on here and other places and there seems to be debate on whether to even use one or not and I'm honestly getting very confused really fast. The last thing I read said that on a disc/drum system with a dual master cylinder, an adjustable proportioning valve should be used. So is this what I need to use instead?:

http://www.speedwaymotors.com/Adjustable-Proportioning-Blocks-With-Brake-Light-Switch,6160.html

 

I'm not clear with your description. Pictures always help. This one is from the link you posted.

What port is leaking? Have you checked the line for problems with the flair? Same for the seat were the line attaches? New parts sometimes leak until you cinch them down a few times. Loosen and tighten a few times to see if that helps. If that doesn't stop the leak take it apart and look at the seating surfaces. That combination valve is correct for disc/drum brakes.

 

sorry, the port that is leaking I've circled in purple:

 

The factory combo valves with fixed value proportioning really should not be used on vehicles that were not designed to have them. (Speedway even states the fixed value combo valve may need an additional adjustable prop valve downstream, all the more reason not to use that combo valve!)) You are much better off using the above adjustable prop valve block if you are using a hydraulic brake light switch, or simply a stand-alone adjustable prop valve. These can be located any where in the rear brake line.

If your master does not have an internal residual to the rears, install an aftermarket 10 lb valve. If the master is firewall mounted, no residual will be necessary to the front discs; if below the floor, install a 2 lb valve to the fronts. (I'm not certain where the master is on a '53 Buick)

 

Right on. Looks like I'll be getting that adjustable valve. Originally the master cylinder was a single and mounted below the floor with a hydraulic switch. but I've now got a dual mc mounted on the firewall and I'm using a mechanical brake switch. thanks for your help!

 

Yep, looks like your diaphragm is leaking. It's rare, but it happens.