Happened in a customer's MKIV. Failure in the EGR block off plate at the rear of the the engine during a sustained 150 mph + pull caused #6 cylinder to run
REALLY lean.
Another pic of the same piston:
Notice the molten aluminium sprayed all over the connecting rod.
He lost that motor to a $4 gasket and some basic maintainence...
P.S. - This was with stock twins, stock fuel, stock everything except a bleeder T.