So far, the company says, 26 cars have been restored at the factory. “We’ve had an American-owned car, a 275 GTB4,” Mr. Rowley said. “They built an entirely new engine, from the carburetors to the sump.”

Tazio de Nicolo, of Saratoga, Calif., who owns six Ferraris, said the cost of restoring his 1968 330 GTS at the factory was comparable to the rehab of his 1965 275 GTS in the United States, not including shipping. Although the American restorer did a good job, he said, he was swayed by “the passion they have to do the right thing” at Ferrari.

During the rebuilding, the car was disassembled, stripped to the bare metal and repainted in the original color, he said. A few gears in the drivetrain needed to be reproduced by the shop there, the leather interior was redone, and the electrical system was replaced.

The Mercedes restoration program grew out of the company’s museum in Stuttgart, Germany, said Michael Kunz, manager of the Mercedes-Benz Classic Center in Irvine, Calif. In 1993, they decided that “we have something very good here, so why don’t we offer it to the public?“ he said.

Mr. Kunz estimated that 600 to 700 cars have undergone repairs or outright restoration in Irvine. “Some of the more rare parts, we can reproduce them because the company was very good about keeping all the drawings of all the cars,” Mr. Kunz said. “We had a hubcap on one of our own cars, a 540K,” he said, referring to a Mercedes from the 1930s, “and we thought it was a total disaster. But in four weeks, we had a new one made.” The price for that hubcap: $600.