One of the hottest automotive brands in China is the one your grandparents may have driven: Buick.

Buick's success in China remains what many industry observers say is key to the survival of the brand, which still seems to be struggling on its home turf in the U.S. — just a decade after it was saved from the chopping block during the financial crisis.

But a combination of Chinese regulations, increasing competition from Asian automakers and rising trade tensions with the U.S. have some wondering whether Buick's luck in China — the world's largest auto market — will soon run out.

About 80 percent of Buick's global sales last year were in China, and nearly a third of GM's sales in the country came from that brand alone. About 64 percent of Buick's sales in China come from vehicles it doesn't sell in the U.S., such as the Excelle sedan, the GL6 and GL8 minivans, the Velite 5 hybrid and the Verano compact car.

There really are a variety of reasons for this, say industry experts. First the Buick name is famous in China. It was the vehicle of choice for many famous Chinese figures in the middle of the 20th century, including some of the country's best-known political leaders.

When GM wanted to begin producing vehicles in the China in the 1990s, the Buick name was the one that most resonated with consumers and the country's decision-makers. GM has also had a fruitful relationship with its local manufacturing partner, Shanghai Automotive Industry Corp.

That all gives the brand a reputation in China that doesn't exist in the United States.

"Buick has a reputation in China as an exclusive, almost elite reputation," said Michael Dunne, CEO of ZoZo Go, a firm that advises automakers on doing business in China. The average age of a Buick driver in China is 32 or 33. "In the U.S., it is something like twice that," he said. "They did a great job of positioning of positioning Buick as a premium brand."

The Chinese auto market is large, selling roughly 28 million vehicles last year compared with about 17 million in the U.S. — but relatively young. GM and other foreign automakers didn't started entering the market in the 1990s.

"The Chinese have never seen Buick when it wasn't doing everything right," said Doug Betts, head of the automotive division at J.D. Power, a firm that tracks the industry.

However, for members of certain generations in the United States, Buicks are among those American brands that lacked the styling, value and quality of competitors coming out of Europe and Japan.

"Our data here in the U.S. says that Buick has been doing a really good job on quality and has been for a number of years," Betts said. "All of our quality metrics say they make really good cars. They also have really good service. But at the same time, it is difficult for them to conquest these customers that have an opinion based on older data."

The age of the average U.S. buyer is also an issue for the brand, something Buick has been trying to address. While many of those buyers are loyal, Betts said, there simply aren't enough of them for the brand to grow. The vehicles are also priced a bit higher than other brands with the same name power.

"When they come back to the used market, that hurts their residual value," he said.

Buick spokesman Stuart Fowle told CNBC that it is not really fair to compare the market in China with the United States.

"The biggest thing to me about Buick in our two major markets is that it isn't the simple apples-to-apples, big-versus-small comparison other media have made it out to be," Fowle said. "Different market sizes, different brand positioning and different product lines all play big roles."

Buick sells not only a greater array of vehicles in China than it does in the United States, it sells at a wider range of price points, including many prices Fowle said are covered by cheaper Chevrolet models here in the United States.

Buick also said it does not put much consideration into comparing one market with another. And Fowle said Buick does outsell some other car brands in the United States.

"Each year we continue to outsell Acura, Infiniti and Lincoln in the U.S. and globally, and that allows us more resources to develop a strong global lineup moving forward," he said.

Still, Buick sales fell 5.6 percent in 2018, a far greater decline than for any other GM brand in the U.S.

Three of Buick's six models available in the U.S. saw year-over-year sales declines in 2018. Sales of Buick's Cascada convertible fell 26 percent, sales of the Envision compact SUV fell 26.5 percent and sales of the LaCrosse sedan dropped 23 percent.

It is not all bad. Sales of the Encore rose nearly 6 percent, and sales of the Enclave crossover rose just over 2 percent. Buick has had some sales success with its recent crossovers, including the Encore subcompact. And perhaps even more encouraging is that sales of a new line of Regal liftbacks, including a wagon, also rose 22 percent in 2018. The whole Regal lineup is bucking a trend — all are in segments that are supposed to be either tiny in market share or in decline.

Buick is arguably in better shape than GM's luxury Cadillac brand, but GM recently said it plans to make Cadillac the brand that will lead the automaker's electrification efforts, so the automaker has some sort of plan in place for it.

Nevertheless, staking Buick's future on China may not be a smart bet over the long term. Government policy in China has increasingly favored the development of a local automotive industry, and trade tensions with the United States could make business more difficult for foreign automakers in the region. China's auto market also endured its most severe slowdown in roughly two decades in 2018.

Furthermore, Chinese firms are learning from more experienced international firms, and J.D. Power data suggests customers are increasingly feeling they do not need to buy a foreign brand to get a good quality product.

"It is going to be hard work to continue to work there and succeed," said ZoZo Go senior advisor John Bonnell. "I don't want to say it is going to be a death trap or anything like that, but you have to earn your pay to succeed."