Here was my reply:
“Grey market” cars are cars that are brought into the U.S. through channels other than factory authorized dealerships. As it applies to classic cars, it was a popular, if not risky practice from about the late 1970s through the mid 1980s. Typically, these were cars that were either unavailable, or very difficult to acquire in the U.S., usually exotic performance cars such as the Porsche 928 you are interested in.
The owner of the vehicle had to receive approval for possession of the vehicle from both the D.O.T. and the E.P.A. The D.O.T. was primarily concerned with issues of conformity to U.S. specifications which often resulted in modifications to items such as lighting and bumpers before they would approve it. The E.P.A. was primarily concerned with environmental issues and often a catalytic converter would be required before they would approve it. Once the vehicle arrived in the U.S., the owner was given a certain amount of time to make the modifications to the satisfaction of the D.O.T. and the E.P.A.
Many owners were shocked at the complexity and cost of these modifications, and simply chose to ignore them. They would then sell these cars to unsuspecting buyers shortly before this time period expired. Upon registering these cars they would receive a notice that the car was not in conformity with U.S. regulations, and that the vehicle had to be re-exported—or worse—destroyed!
The seller of this “grey market” Porsche 928 claims to have the proper “releases.” I would check them carefully. I would also check the vehicle's registration history. If it has been registered in the U.S. for many years, chances are everything is O.K.
However, I’d be more concerned about the “good amount of work” the car needs, as they are notoriously expensive to repair. I’m a big fan of these under appreciated supercars (having owned one), but the cost of repairs could easily exceed the value of the car, particularly a “grey market” car.
Contact Steve: firstname.lastname@example.org