I called the dealership and have an appointment to have the leaking brake reservoir looked at.

However, today I noticed that in addition to it seeping around the seam in the middle, the electrical connector didn't have the harness attached. I looked around, and sure enough, I found the unattached harness tucked in among the other wires. I reattached it, started the engine and ran the system test via message center. Everything checked out good. That's when I realized that the brake system checked out good even with the harness disconnected!

Apparently this harness was never attached at the factory.

You might want to check yours....

 

are you sure that connector needed to be connected..???

 

Well, the harness was hanging loose, and the connector on the reservoir didn't have a cap over it to suggest nothing should be attached to it, so I'd guess it was supposed to be attached.

Is yours attached?

 

Just an update. I took the car back to the dealership yesterday, and they are replacing the master cylinder. Unfortunately, they did not have one in stock, so they had to keep the mustang. The Focus they gave me as a loaner (they were willing to upgrade me to a Taurus no charge, so it never hurts to ask!) will stay in the driveway until I get the call to pick the mustang up.