Shares of Sears Holdings tumbled as much as 13 percent Friday, skidding to a record low after the company disclosed earlier in the week that a hedge fund owned by CEO Eddie Lampert offered to buy the troubled retailer's Kenmore appliance division for $400 million. Lampert's hedge fund, ESL Investments, also made an offer to buy Sears' Home Improvement business for as much as $80 million in cash, both companies said in a filing with the Securities and Exchange Commission on Tuesday.