(FORTUNE Magazine) – For the past several years, U.S. automakers have been struggling to prove that they can sell cars in Japan. They have invested tens of millions of dollars to reengineer cars for the Japanese market by moving the steering wheels to the right-hand side. They have invested further millions to develop their own dealer networks. They have even importuned Toyota and Honda to sell Chevys and Jeeps for them.

Japanese consumers have largely ignored these efforts. Instead, they insist on buying an American vehicle that Detroit doesn't really want to sell them: the homely Chevy Astro. A boxy, low-tech van with left-hand drive that's widely ignored in the U.S., the Astro has developed a passionate following among affluent Japanese yuppies. But GM imports only a handful of Astros into the country. More than 80% of the van's sales are made through a shadowy network of independent importers in what's known as the "gray market," where prices are substantially cheaper.

Exact sales figures are hard to come by, but it is estimated that about 14,000 Astros were sold in Japan last year, making it the most popular American vehicle. In second place was the Chevy Cavalier, distributed through Toyota dealers, which achieved sales of 11,500. The Jeep Cherokee finished third with sales of 9,800. According to Steve Yum, a senior consultant for J.D. Power & Associates in Tokyo, young families buy Astros for auto camping--driving to a rural area and plugging into an electric socket at a camp ground.

Since stock Astros have all the pizzazz of a breadbox, the Japanese customize them with fancy paint, running boards, fog lights, raised roofs, and body skirts. Behind tinted windows, the interiors are done up Las Vegas-style with upholstered ceilings, copious wood-grain trim, and dozens of lights. Several Japanese language magazines with names like Deuce and Daytona feature ads for new and used Astros, the more outrageous the better. "It's almost like a cult vehicle," says Linda Pesonen, the Detroit-based assistant brand manager for the Astro.

Astros sold in Japan through official channels start at $41,000. Since gray-market dealers keep inventories low and avoid costly overhead, prices start at about $35,000, and dickering can knock off another 5% to 10%. But caveat emptor: Gray-market cars aren't covered by factory warranties because the vehicles aren't sold through proper channels. Service and repairs can be a hassle because fly-by-night dealers aren't equipped to handle them.

So far, GM hasn't exactly been bragging about the Astro's success. Gray-market sales divert business from GM's official importers, and GM occasionally has to deal with angry gray-market customers who complain when they can't get service. In fact, GM is trying to limit gray-market sales by policing dealers in port cities on the East and West Coasts, where most of the vehicles originate. It has also stopped allowing Japanese tourists to buy Astros in the U.S. and take them home.

None of the Astro's popularity in Japan has spilled over to the U.S., where 125,000 were sold last year, for $22,000 to $26,000. GM does little promotion and hasn't redesigned the van in 12 years. Buyers tend to be commercial users like florists and locksmiths, or working-class families whose head of household is 45 or older.

The Japanese have developed a peculiar taste for other offbeat American vehicles like the Chevrolet Caprice and Dodge Ram van, which should cause U.S. automakers to rethink their strategy for selling cars in Japan. Instead of going to the trouble of reengineering and building dealer networks, maybe they should just dump cars into the gray market--and then get out of the way.

--Cindy Kano and Alex Taylor III