Thanks for all the suggestions. Diving Pete, one of my worries was that I installed the seal backwards, but I don't actually think it's possible with this kit as the seal is attached to the top of the spring. I've been going through old pictures trying to figure out what I missed, and I bet this is it... And I may have wasted some of your time reading through that. I haven't pulled up that little tab to verify that second port isn't clogged. In fact, I forgot about it. When I started this, the MC was caked in crystallized brake fluid. That vent being clogged would seemingly explain the behavior. Will give this another cleaning and verify that that hole is not clogged. This time with a long soak in solvent, then ultrasonic, and then I'll run fishing line through that hole. raYzerman, if I can get this operating correctly, I'll try to the zip tie method to drain out remaining air. I've never done that before. I don't think this is the issue since the pistons and seals are new, and they're sliding well. This is good to know though because I'm certain I'll run into this in the future at some point.