GMPartsGiant.com offers the wholesale prices for genuine 1991 Buick Regal parts. Parts like Automatic Transmission Oil Pump are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 6 Cyl 3.1L, 6 Cyl 3.8L. Model Code: 2 DOOR, 4 DOOR, CUSTOM 2 DOOR, CUSTOM 4 DOOR, LIMITED 2 DOOR, LIMITED 4 DOOR.