I use Mobil 1 in the HHR, and we use that or Royal Purple in just about everything we have that we buy new, or fairly new. Now, we've used regular Pennzoil 10w30 in my truck since the motor was rebuilt in about '97. That is one clean engine.... Has about 70k miles since the rebuild. Oil changed about every 4k miles on it, but since I have usually once or twice a year since I don't drive that much.

Needless to say, synthetic may be better, but you sure aren't hurting anything with dino oil as long as you change it. My Lumina is the same... Has had Valvoline since new, then Pennzoil since I bought it. When I took it in to have the head gasket fixed, the tech was amazed at how clean the engine was for a car that old with that many miles. Again, this car had the oil changed every 3k.

Like I said, just keep up on the changes, and you're not going to hurt anything. I would just advise not to switch to synthetic if you have a leak. Not sure why, but it'll make the leak worse. My guess is it cleans out some gunk or whatever is built up around the leak making it a bigger hole.

 

Syn oil molecules are smaller than conventional oils and will pass through gaps eaiser.

Both have large amounts of detrergent in them and one does not un gunk much more than the other. Syn will be less likely to gunk though.

Older engine will leak easier vs new ones that are sealed better.

 

The myths about putting syn oil in engines raised on dino oil were dispensed with 30 years ago, but like most urban legends, they die hard. There was a grain of truth going back to some ingredient in the original Mobil 1 formulation interacting with certain materials, but that was fixed decades ago.

I have put various syn oils in any number of used cars that had been run on dino oil without incident.