It seems like a 'oil additive technology has changed and we are updating our labeling to align and allow us more flexibility to adjust trace elements based on availability and cost' than the manufacturers actually changing the hard oil base ingredients.
I once sat next to a senior chemist from Exxon-Mobile at a conference over a beer and I asked him about synthetic oils and he asked if I am talking about SYNTHETIC or Synthetic,
Synthetic is not SYNTHETIC
SYNTHETIC oil is the base oil/slippy stuff that does add some leakage if your seals are shot or old
Synthetic is what you get when you buy 'synthetic blend' and is just the sub trace elements that are put in
Besides, I have come to a different viewpoint on the whole 'ethanol and synthetic oil are causing all these problems' train.
Yes, if you put e85 in a 40 year old, un-serviced fuel system it's going to show you where all the things are worn out. Same as putting synthetic in your 40 year old SBC. The seals are shot and dried out. The ethanol/syn oil didn't cause your seals to fail, it just exposed that they were shot.
If syn oil was causing all these leaks, why is the bottom of 75% of old cars covered in oil/grease/muck after 2 years on the road and never had syn oil installed but 10 year old cars built recently don't? It's not because the syn oil caused the leaks, it's because rope main rear seals and cork gaskets sucked. My FIL's 64 mustang got OE quality gaskets on a rebuild and leaked like a sieve until it got re-gasketed with steel core, molded silicone modern improved gaskets.
It's like if you have a worn out tire that is out of balance at 78 mph. If you drive 75 or under all the time you never notice the out of balance. When you go 80 and it starts shaking it's not like the tire decided to fail at 78, you have just never put it in a condition that causes it to exhibit the out of balance. That doesn't mean that the tire was ever not out of balance.
Also dirt builds up around old seals and create a false seal which synthetic can wash away and expose a faulty seal. Seals will last longer if they have been ran with synthetic their whole service lives. Good for newer stuff but bad for older stuff that ran on conventional oil for years. Overall, the auto industry doesn't give a flip over old stuff, they rather you junk it and buy new with lots of loans.