[jocko]

I would check the rear brake outlet of the mc (ie disconnect where it enters the distribution block) and check for flow when you depress the brake pedal (unless you’re saying that is what you already did - I wasn’t sure if “at the rear brake” meant at the rear wheel or at the mc rear brake system outlet port). If no flow, it’s an mc issue. If good flow, I suspect the distrib block shuttle valve is not centered or the block itself is somehow clogged/faulty.