Okay here's the deal with the zinc additive and the M103 engine.

To begin with the zinc additive is much more necessary during the cam and lifter breakin period than it is in a high mileage engine. Added to that is the fact that the M103 has what is called a sliding mechanism, not as much load concentration as is found in a flat tappet Ford or Chevy V8.

The universal grade (diesel) oils have other redeeming qualities. One is added detergents that will keep a gas engine squeaky clean inside. The Total Base Number test commonly performed on oils comes back with a VERY high number for Chevron Delo and I expect also with the other commonly used universal grades (Rotella and Delvac.)

Now for the testimonies such as "I've used nothing but my precious brand X for 25 years and my engines have lasted forever." That's all very nice except those oils DID have zinc additive in them until just a few years ago. At some point just a few years ago, the engine oil producers saw a way to justify a little extra profit for themselves. They justified the elimination of the zinc additive with the fact that all modern auto engines have roller followers thus not requiring it any more. Did they TELL you that they were dropping it out of the oil? I don't know about you, but they never told me. They just said the heck with those old Farts that drive old cars.

Since they just quietly started leaving out this ingredient, only the last FEW years of that "25 years and my engines run forever" period has been without this ingredient that is life blood for older engines without roller cam followers.

If you drive a car with no roller cam followers, use an oil with the zinc additive included. Do NOT add zinc to the oil with the exception of the break in period after cam and follower change. The reason is that too much of it can cause a sludge problem. The oils that use zinc as part of the blend are carefully formulating the balance of zinc additive with the amount of detergents. Don't try to home brew and achieve this balance. You don't have the lab that your sacred favorite oil maker has.