The "Approved Lubricants" table of the Owner's Manual (p. 58) lists the following :
B.P. : Visco-Static Longlife
CASTROL : Castrolite
ESSO : Esso Motor Oil 20W30
MOBIL : Mobiloil Special 10W30 - 20W40
SHELL : Shell Super Oil
Waples for old engines recommends Mobil DELVAC 15W-40 or Shell Rotella-t heavy duty truck oils. This oils contains a good antiwear and anti-corrosive agent called ZDDP (zink dialkyl dithio phosphate).