I have personally saw SEVERAL engines dissassembled at my Dad'* shop that ran synthetic oil only. Synthetic oil ... like on the commercial .. doesn't burn. Try it sometime.
The walls of the cylinders are coated with a thin coat of oil by the oil ring each time
the piston goes up and down. If it doesn't burn, it turns into a syrup like goo.
This tends to clog up the oil ring. I've saw it several ( like 8 or 10 ) times. Now, other factors could be involved I don't know. I do know the 'vettes that use synthetic oil as recommended by GM had special oil rings. Anyway, just my 2 cents.
I think Synthetic is great when an engine is designed to use it. I think it'* bad for the long term when it isn't. Consumer Reports has published proof of this before.
1992 SSEI Bonneville with all the options except heated windshield and ride control.
Mods Include 1998 SC'd Delco Ignition with Belden wires.
Autolite 104 plugs ,180 degree tstat
K&N Filter with ricepipe, 2.3 inch pulley with ZZP idler
Ported exhaust headers, Poly end links.
High flow cat. TPS tweak, Boost bypass mod
High low fan override.
" Always try it yourself. I bet the guy you pay to repair it broke a few before he fixed your'*. "