Rite Aid, the No. 3 drug retailer in the nation, unveiled in April a huge financial restructuring plan designed to restore the company to health, following a series of earnings shortfalls resulting in part from the company's aggressive expansion starting in the mid-1990s. Rite Aid shares tumbled immediately at the market's open and were down 7/16, or 7%, to 6 1/4 in morning trading. Rite Aid finished regular trading down 5/8, or 9% at 6. Since January 1999 when Rite Aid bought the unit, Rite Aid's stock has dropped 87%. Under the terms of the deal to sell PCS, which provides drug benefit management services to employers and health plans, Rite Aid will get from Irving, Texas-based Advance Paradigm $675 million in cash, $200 million in senior subordinated debt and $125 million in new equity. Advance Paradigm will change its name to Advance PCS and will become the country's largest pharmacy benefit manager with nearly 75 million customers.