Thanks for the reply. I dug around in my reprint of a service manual and I think what I have is strictly a warning lamp switch, not an actual proportioning valve! Although all the brake lines do run through it before exiting to various wheel cylinders.
Hijack my own post now: I wonder if I could just get a proper disc/drum style master cylinder and not use a proportioning valve? That way I could reinstall the warning lamp switch and ditch the leaky aftermarket part.
Thoughts FABO folks?