There's a turbo, but no intercooler; unless it was behind the front bumper like the GTS, but that would mean the intake manifold would also have to be reshaped and, besides, I think the GTS was presented in '81—2 years away from that bit of engineering. And not only do they not provide a VIN, curiously, the numbers should've have been on the right side of the firewall.
So unless this famous German footballer got an in with Porsche to make him a special "pre-production" 937 tagged GT-L (comfort group) with request to replace the red pin stripes on the seats with white, I'm not sure where else to look for an answer. It even has hood shocks, I suppose that maybe part of the comfort group since it's much too uncomfortable to fumble with a hood stay...and there's a risk getting your hands dirty.
Nothing makes sense...but the price suggests this 924 may be something special after all. Anything's possible with Porsche, so the search continues.