Full synthetic oil:
>>Pros: premium performance at low and high temps, clean engine, no build up
of residu because of impurities of the oil. Due to purity of synt.oil it
can cope with longer intervals between oil changes. Less oil breakdown.
The engine may or may not leak due to the removal of residu from previous
Dino oils, and thus making room for more leaks, especially seals and
gaskets. It is recommended to stay with same brand in order to avoid
different additives and solvents that have negative effects on seals and
o-rings. So if your seals are in top condition, you're ok. With bad seals
the crud may just prevent more leakage, and cleaning out will increase the
leaking. The older Mobil-1 0w15 is known to un-swell the seals causing leaks,
but the engineers fixed this by altering the additive package some time ago.
>>Cons: you may reconsider using Synth. when already experiencing leaks and
want to avoid the chance of more leaking. You can still switch back to
Dino without big problems but this will not reverse the leaks. Try to stay
within one brand to avoid other solvents working on the seals. This is one
of the reasons that full.Synth gets blamed for leaks. The full Synth is
the most expensive choice.
So the advice: Use a good Synthetic oil (Mobil 1 ?) when the engine seals are in good condition and money is not an issue. Always use oils from the same brand in the engine regardless of Synthetic or Dino.