GREYHOUND <G> BUYS GENERAL MOTORS <GM> BUS UNIT Greyhound Corp said it has signed a definitive agreement to buy General Motors Corp's U.S. Transit Bus and Parts business for an undisclosed sum. The agreement, tentatively set in January, includes production tooling, design and equipment for urban transit buses, inventories and trademark identification. The agreement also incudes the right to buy GM's Canadian Transit Bus and Parts business, contingent on a satisfactory labor agreement. Greyhound said it will relocate the production facilities, currently in Pontiac, Michigan, to an undetermined location.