Concerning Syn oil....

It is great stuff for a lower mileage car, but as the miles increase the seals start to wear. 'High Mileage' oils take this into consideration and the molecules are bigger so they will not slip by the seals.

Syn oils ALL have very small Molecules and this is one reason they lube your engine better. But these will slip pass worn seals to the point you will wonder why your crank seal has suddenly started leaking.

If you can afford to roll the dice on a crankcase full of Syn oil then go for it. If you suddenly develop oil leaks from every seal then you will just have to go back to Dino oil.

We used to test Syn oil to 250,000 miles and then tear down the engine. There was usually no wear, so the stuff is worth using if you can use it without losing it all past some worn seals.