Thanks for your replies and your excellent advice.
I've just ordered two oil sample kits from Wearcheck. The Wearcheck representative was very congenial over the telephone.
Although the $14 price of the MOB-1 kit is very reasonable, I decided to purchase the $24 MOB-2 kit for the additional information that it provides, including the total base number.
Wearcheck does provide a bargain by including sulfur content analysis in its basic testing service. Many of us have older vehicles and are interested in sulfur content as a rough indicator of the oil's compatibility with copper alloys.
I'll post the virgin oil analysis results when I receive them. Thanks again!