[HarryD]

Sugarwood has some good points but...

The whole reason the zinc and phosphorus (ZDDP) issue came up was due to engine builders seeing excessive cam failures (mostly on high performance engines) after the oil makers changed to the API CJ4/SJ (and subsequent updates) standards. At that time, ZDDP was reduced to extend catalyst life. This change mostly affected the xW-30 and xW-20 oils but would sometimes also affect the 15W-40 and 20W50 commonly used in our cars.

The reason newer cars can tolerate lower ZDDP levels has to do with the change to the tappet configuration from flat tappets to a roller tappets. This changed occurred in most all new cars in the mid to late -90's as part of the car makers quest for improved gas mileage.

And while the story is more than ZDDP, this is the primary reason for concern. There are many oils that are still ok for our older, flat tappet motors. 15W-50 Mobil 1 is one. Driven GP-1 is another. Most 15W-40 diesel oils are also ok. There are others as well.

Get a good oil made for older cars. As noted above the leaking issue with synthetic oils was an issue many, many years ago but has been resolved.

To add to the confusion, you can get Dino, semi-synthetic, and full synthetic oils. The differences have to do do with whether they use petroleum (dino and semi-synthetic) or synthetic materials for their bases.

I used Brad Penn and it's descendants (PennGrade) until recently with good success. When my motor was disassembled a while back for a top end issue, no excess wear was detected with 150,000+ miles other than the damage due to a backfire. Recently, based on information from LN Engineering and a local well respected engine builder, I switched to Driven GP-1. These guys were my source for the Brad Penn recommendation as well which served me well until now.

But as I tell every one, your car, your money, your choice.