The ratings on Memphis, Tenn.-based AutoZone Inc. reflect the company's leading position in the stable, but highly competitive, retail automobile parts aftermarket; consistent operating performance; and strong profitability measures. These strengths are somewhat tempered by management's aggressive share repurchase activity, which has increased leverage on a steady basis. AutoZone is the largest retailer of automotive parts in the U.S., with approximately 3,300 stores in 48 states and another 55 stores in Mexico. Although consolidation in the industry has resulted in five players maintaining significant market share, AutoZone remains the largest and most geographically diverse in the U.S. This allows the company to take advantage of economies of scale in purchasing and advertising. The company's core do-it-yourself market has grown about