Friends car at racetrack today.
Experience racer, and darn good mechanic.
2008 Z06

New front pads, and new stock calipers. New pins.
New rotors
Complete brake flush, excluding Tech 2 cycling of abs
Had a fulll ABS bleed maybe 3 months ago, not related to current issues, just because friend was there with snap on too, that could cycle ABS>

First problem about a month ago, in a race the pedal suddenly went to the floor and no brakes.
Everything a bit old, so all new parts as above.

His first run today, pedal goes major spongy after a couple of laps... comes in and front brakes are cooking.
Pads are dragging.
Brake bleed, no help. Still dragging, as can't turn the rotor by hand - both front wheels.

Pulled the new pads, put in old 1/2 worn pads.
Still the same.

Put the old caliper back one with the old pads, still the same, after brakes have been applied, pistons not retracting into calipers.
Pedal goes 1/2 way to floor, spongy, but can pump it up where the 1/2 way point is firm -- of course rotor can't be turned by hand.

Had scanner on the car, no codes for anything.

So -- master cylinder ? ABS?

Engine not running, so not power booster.

 

caliper's not installed upside down on wrong side of car are they?

 

LOL
Figure it's the master.
Easy replacement, except for needing a tech2 to cycle the abs.

 

I wish I could help you, sorry. It seems to be a rear issue. I never heard of anything like this. I'm wondering if it's electrical rather than mechanical.