Martin H. Dubilier, 65, chairman and co-founder of the investment firm Clayton & Dubilier. An inventor as well as an investor, Dubilier invented a rust-resistant toy train track as a child and sold it to Lionel. As a teen-ager he also invented a low-voltage flash bulb that made battery packs unnecessary. He formed his investment firm with L. E. Clayton in 1976 and two years later turned to leveraged buyouts of troubled companies. Among the companies the firm acquired were Uniroyal Goodrich Tire Co., which it later sold, and Lexmark, the supplies branch of IBM. On Wednesday in Greenwich, Conn., of lung cancer.