I've never understood a synthetic blend
The whole point of a synthetic is to insure a consistent molecular weight at the atomic level - without some of the errors that traditional distillation introduces in conventional oils, which allows for some different viscosity and wear characteristics. And that's ignoring the properties of different base stocks (hydrocracked, polyalphaolefin, ester). Why would you add something with an inconsistent MW to a mixture of a consistent MW, that would then have a (slightly) different molecular interaction with things like metals, engine debris, moisture, fuel contamination, and seals?
It just strikes me as an odd combo. Seems to be a cost closer to synthetic with material properties closer to conventional. When I worked at Sears, the valvoline rep told me their semi-syn base stocks were 40% syn, 60% conventional. Take that with a grain of salt as I've been able to neither validate nor deny that word of mouth statement.
Anecdotally, for what it's worth, my rig has had synthetic since day 1 from the previous owner, and I've continued the trend over. I've had gaskets off for other maintenance so I'll try to summarize how it's treated me
- 10/16, 116k. R&R intake manifold gaskets. Valley pan gasket, knock sensor grommets found to be in good shape. Gasket material still pliable, noted no leaks from knock sensor. Slight darkening of material in the engine that would not wipe off with brake cleaner. No deposits or discoloration noted on camshaft.
- 3/19, 139k. R&R oil pump. Pickup tube o ring, oil pan gasket, front cover gasket, in good condition - material still pliable. Front crank seal stiff, but not leaking. Noted slight brown discoloration on exterior surfaces of oil pan, minor discoloration in recesses of rockers when viewed through oil fill cap. Suspicion of short trip moisture accumulation. Shortened OCI, problem has since resolved.
- Today - 146k, rear main, rear cover, valve cover gaskets are original and have not been removed. Can't comment on gasket condition but there are no leaks or wet spots.
Edit: Never done a series of UOAs to compare wear between different oil so I can't comment on that. I'll grab one probably in 10k or so just as a check up, however.