Run a quart of engine flush at the next oil change, and refill with either straight 30 weight detergent oil or 15W40 diesel-rated oil. The engine flush will clean out any sludge in the lifter check valves from running QS oil, and the 15W40 has a slightly thicker basic viscosity to keep the leakdown to a minimum. The original reccomendation for these engines was straight 30 weight in the summer, and 20W in the winter. Variable-viscosity oils didn't even exist until the mid-1950's.
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!