Most of us use 15W-40 Diesel rated oil in the old engines. It seems to do a good job of lubricating, and the 15 bottom weight number seems to be a little less likely to leak than the 10.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!