The highly profitable European unit that helped prop up General Motors Corp. during the recent U.S. recession suddenly doesn't look so invincible.</br></br>With some aging product lines in key segments and tougher competition in Germany, France and Italy, GM's European unit lost market share in the third quarter, slipping to 11.8% from 13.1%. During the first nine months of the year, GM Europe's sales volume grew, but trailed the market as a whole. Among GM's new problems in Europe, where it has led rivals in controlling costs, is a resurgency among Ford Motor Co., Volkswagen AG and Fiat SpA.</br></br>The setbacks in Europe, which GM maintains are only temporary, couldn't come at a worse time. As its third-quarter results indicate, GM is undergoing a long, slow turnaround in North America. Although the auto maker narrowed its loss in North America, it still was $296 in the red for each vehicle sold. By contrast, Chrysler Corp., which posted record earnings for the quarter, had a profit of $1,000 for each vehicle.</br></br>Investors continued to punish GM's stock Friday, a day after the company reported its disappointing third-quarter results. It fell $1.875 a share, or 4.4%, to close at $41.25 in New York Stock Exchange composite trading.</br></br>More analysts lowered their estimates for the next couple of quarters, saying GM's cost-cutting efforts may have plateaued. As a result, they said, it is unlikely that GM's debt ratings, which trail those of its domestic rivals, will be upgraded anytime soon.