DETROIT/SEOUL, Oct 22 (Reuters) - Hyundai Motor Co said on Tuesday it would expand a U.S. recall of about 27,500 Genesis sedans to South Korea and other markets to address a potential brake issue as it prepares to unveil a new version of the large sedan as early as next month.

Hyundai said it is recalling the cars, which were built from April 1, 2008, through March 16, 2012, to replace the brake fluid. The company declined to specify the other countries that could be affected.

While the United States and South Korea are two of the biggest markets for the premium sedan, the issue is unlikely to have a serious effect on sales. It does however come as Hyundai tries to rebuild its reputation after a massive recall in April that affected more than 2 million cars sold by Hyundai and affiliate Kia Motors Corp.

The company had already initiated a service campaign in March to replace the brake fluid in the affected cars as they were brought into dealers. The fluid had been replaced in about 60 percent, or about 40,000, of the vehicles, a spokesman said.

However, after receiving word that U.S. safety regulators had opened an investigation into an estimated 40,000 Genesis cars from model year 2009, Hyundai decided to recall the rest, the company said. Letters will be mailed to the affected owners starting next month.

Owners will be instructed to bring their cars to Hyundai dealers for brake inspections and changing of the brake fluid with replacement fluid containing an anticorrosive additive, the Hyundai spokesman said. There will be no cost to the owners.

U.S. safety regulators at the National Highway Traffic Safety Administration had opened a preliminary evaluation into an estimated 40,000 Genesis cars from model year 2009 after receiving 23 consumer complaints alleging reduced brake effectiveness, according to documents filed online. Several complaints said the problem was diagnosed as a faulty antilock brake system module.

In one complaint NHTSA received, a consumer in Florida alleged that her brakes did not work, resulting in a crash into another vehicle stopped at a red light. In another complaint, the consumer reported responding to the same problem by using the parking brake, which caused the driver to lose control.