I may not be able to speak to the properties of the Valvoline syn blend, but I have experimented with a syn-blend vs. Maxlife.
I did a controlled experiment with a few types of oils, Pennzoil Conventional, Castrol Syntec blend, and Maxlife. I filled three cups with the oils, each cup containing a 2" piece of old valve cover gasket from 2.3 ford L4 and one of the oils.
I had my girlfriend and nephew examine(for an unbiased opinion) each of the pieces of gasket after they had been submerged for 4 weeks, they both noticed that the maxlife was the only oil which physically softened(not swelled) the gasket material, the Syn blend and Pennzoil Conventional did virtually nothing to change the properties of the gasket compared to the control piece.