When U.S. servicemen purchased new cars while stationed in Europe, they placed their orders at the base PX. Bob explained that salesmen employed by local German (or, in the U.K., English) dealers sold cars on commission at PX and BX offices. There were salesmen for each American brand: AMC, Chrysler, Ford and GM. That's how they got the same prices or better than they'd pay in the U.S.: no shipping fees, tariffs, nothing. "Buy American" was very important at the time because of the "dollar drain" and the cost of the Viet Nam war. Buying American-made products kept dollars out of foreign hands. The U.S. Army imported American products, even Miller High Life beer, for the GIs overseas during this time.
The local German dealers got their commission from the sale along with the salesmen, but from the point when financing was in place, GM Overseas Delivery (GMOD) was paid directly and the car was delivered directly to the service member stateside or overseas. The local dealer, whether in the U.S. or Europe, was only obligated to do dealer prep if the new buyer requested such service. The foreign dealers had nothing to do with the delivery of the vehicle and all vehicles were built in the U.S. to U.S. specifications. Because these vehicles were being delivered overseas, but not for foreign sale, they did not need the certification plate required by the foreign governments for importing completely knocked-down (CKD) units or single unit packs (SUPs). This also explains why the RPO V78 "Less Certification Plate" entry appears on their window stickers.
So how was a car "delivered directly" to a serviceman stationed abroad? Through his agent—the Military Sea Transportation Service (MSTS). After 1970, MSTS became the Military Sealift Command. The MSTS took delivery of the new car directly from GMOD, which had delivered it to the closest Stateside port where MSTS was receiving other DOD materials (like that Miller High Life beer), in a special duty free area. Orders and paperwork were already in place with MSTS by the time the car was delivered to the MSTS terminal. MSTS transported the car to the port nearest the serviceman's station, where he was able to pick it up (with the correct paperwork, of course).
In the '60s and early '70s enlisted men had to pay to ship their cars, while senior non-commissioned officers (NCOs) and officers got one car shipped over and one shipped back free of charge. MSTS was much cheaper than other services and the only way to get a car delivered without customs hassles, so was the favorite of the enlisted men.
Once in Germany or the U.K., the cars were serviced at the local PX or BX service stations that were near larger bases, but warranty work was usually done at the local GM dealer (Opel in Germany and Vauxhall in the U.K.).
Interestingly, Dave has some documentation that shows there was more than one way for a U.S. serviceman to purchase a car while overseas. For example, there were ads in a local German newspaper aimed at U.S. servicemen, and they talk about handing all of the paperwork of the transaction, price matching to that of the PX, etc. He also has some local dealer literature that is clearly marketing to servicemen.
Bob remembers this situation well. He recalls that such arrangements came and went and some were scams—thinly disguised ways for naive GIs to import cars duty free and then flip them back to their "agents" for quick profit from the sale of the car to locals at a lower than foreign dealer price. GIs were encouraged to use the authorized PX/BX sales staff because so many servicemen got caught up in this kind of scam. This situation was like selling duty free cigarettes, bourbon and stereo equipment for profit, but cars were much bigger ticket items. It was one of the reasons there was a German police liaison office at the bigger bases to deal with this sort of thing. Bob has at least one such ad in his collection that was aimed at German buyers who wanted to buy "gray market" American cars without going through the local authorized GM dealers.
As Bob mentioned above, even servicemen in the U.S. could buy their cars from some PXs. Dave said that for years, this was a bone of contention between U.S. car dealers and the manufacturers, who let the military do it. The dealer near the base would get a $50 courtesy delivery fee and maybe some service and warranty work, but no other profit on the sale. This led some dealers to offer military discount prices in an attempt to get the business.