No need for high ZDDP oils in these old red blocks. Or for that matter in a lot of other engines where people seem to be wringing their hands about it. The approx. 800PPM of zinc and phosphorous in the latest (API SN) oils is plenty to protect your nicely broken-in Volvo.

But you may want to consider 5W30 as your "winter" oil, as it has the same hot viscosity as 10W30 but will flow and lubricate faster at cold startup. For what it's worth, I use it year round in my 1983.

Some good info in this link, from a GM powertrain and lubricants specialist. The whole paper is interesting, but the ZDDP part is contained in the "Starburst Oil Myths" section. http://www.nonlintec.com/sprite/oil_myths.pdf
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Son's XC70, daughter's XC60, my 83 244DL, 89 745 (Chev LT-1 V8), and XC60. Also '77 MGB with Chev V6, and four old motorcycles. Long gone: 1981 244, 1994 940 and 1998 S90.