Hi Chris,
Getting a one-way ticket for the Kampu Ferry proved to be a lot of work. We arranged the ferry through Nippon travel agency in the main train station in Kobe where the assistant manager fortunately spoke reasonably good english and she kept calling and faxing to the Kampu Ferry people. Kampu Ferry insisted on treating the car as cargo but after a dozen phone calls they relented. They actually contacted the customs agents that cleared the Carnet and called to customs in Korea as well and they wanted copies of all the relevant documents faxed to them (Carnet, car registration, international drivers licence etc). All in all it took us seven visits to the travel agent and only thanks to their persistance we got the one-way ticket. Fairly cheap as well, around 250 euro if I remember correctly for the car + driver and one passenger.
Another interesting thing happened on arrival in Busan. As it turned out the customs people there had never seen our type of Carnet (issued by ADAC in Germany). Supposedly the only type of Carnet they accept is an ATA Carnet. In all it took about four hours of discussion, answering hundreds of questions and researching every single document we had before they finally approved our entering with the car. They were all very friendly but it was a bit disconcerting to think that they could easily have made a different decision.
Anyway, we loved Japan very much, what a great country and Korea is very nice as well so it was definitely worth it.
Bye,
Onno