I do actually indeed suggest that you pop the other MC in to see what happens. It's already sitting there, so why not try it? I am a mega gearhead, and would definitely install the alternate MC myself to see what may happen before moving forward with anything else, especially as easy as it is to do a back to back MC swap out (providing you don't have to get into brake line port adapters or any changes with the brake lines).
TIP: Absolutely positively thoroughly bench bleed the MC first (off of the car literally in a bench vise, of course, right?) - view the links below. I strongly suggest the port plug method as opposed to the old school hose method for MC bench bleeding (it's vastly more conclusive than the hose method). Once that is done: Air does not go down brake lines when a MC is disconnected. As such, place a big fat towel underneath the MC to catch the brake fluid, disconnect the lines from your current MC, cap the brake lines with some generic vacuum caps for the moment. Yank the (dripping) current MC out (plug the ports quickly if possible to prevent the mess). Bolt the new MC in with the bleeding port plugs still in place. Now yank the little vacuum caps off of the brake lines and plug them into the new MC as quickly as you can, BUT do not tighten them down all of the way. Why? If you wait for both loosely connected lines to start steadily dripping, this has bled this part of the braking system out, not requiring you to get into a full on four wheel brake bleed session again (unless you believe there could be air still strapped somewhere in the system).
http://hydratechbraking.com/braketech1.html
http://www.hydratechbraking.com//ima...BleedSheet.JPG
Let us know how the alternate MC behaves - we're all here to help!
