In Reply to: What oil should I use? posted by Beth and Allen on December 21, 2017 at 23:09:03:
IMO. The syn oils run a higher detergent and can clean out the varnish etc behind the seals and gaskets possibly causing a leak IF it has not been maintained with syn oil. 30K miles is not far enough out of the realm of running syn oil. 2004 means a lot of those seals (rear/front main) have probably dried out and syn oil is going to leak. Would I put syn in it? Probably. And I would also be aware that it might start leaking like a sieve and cost me a few bucks to re-seal it. After that syn oil should not be a problem at all.
If using dead dino oil, I would recommend the Mobil brand, Not the syn oil as they are famous for, but the run of the mill dead dino oil that they also produce, if you can find it. I would steer far away from Shell or Havoline, IMO.