PURCHASE AGREEMENT BY AND AMONG WELLS FARGO BANK, N.A., EVEREN CAPITAL CORPORATION, BFLX LEASING HOLDINGS LLC, GATX RAIL LOCOMOTIVE GROUP, L.L.C., GATX CORPORATION (SOLELY FOR PURPOSES OF ARTICLE V, SECTIONS 6.5, 6.6, 6.7, 6.9(a), 6.10, 6.17, 6.18,...