Les, do you have SS brake hoses? I'm wondering if the OEM rubber hoses are as bad as the rest of the German plastics are.

Or maybe the caliper pistons get stuck or leak after sitting?

Dave, I was wondering the same thing so with the car running I pulled the vacuum hose from the booster and the pedal firmed up again. Probably because it takes 2000 psi to move the brake pistons.