Re: 6.0 braking problem NEED HELP!
When you pull out the defective MC again, put it in your vice, plug up the line outlets with either plugs or a U shaped piece of line, fill the MC with fluid, cap everything tight and push the plunger in. If it slides in easily, your cups/seals are shot and it is just "wading" in fluid in the reservoir. If it operates with extreme resistance, then your problem is somewhere else like a proportioning valve.
Either way, I would buy a name brand, top quality MC instead of those at O'Reilly's.