On May 17 the Mariners, seeking to stabilize the top of their lineup, took a chance and agreed to sign 41-year-old leftfielder Rickey Henderson. In his 22-year career the much-traveled Henderson, who had worn out his welcome with the Mets and been released four days before joining the Mariners, has put up some staggering numbers. Consider: He's third alltime in walks (1,999) and trails leader Babe Ruth by only 57; he's fifth in runs (2,124) and just 121 behind leader Ty Cobb; he and Cobb are the only players with at least 2,000 runs, 1,000 runs batted in, 1,000 walks and 500 stolen bases; and he's one of four players with a career on-base percentage over .400 and more than 10,000 at bats. Then there's stolen bases. Through Sunday, Henderson, the career steals leader, held a greater margin, measured by percentage, over the second man on the list than any other leader in a major career statistical category.