Shell Rotela. I use it exclusively. It is intended for diesel engines, but superior for otto (gasoline) engines as well. Last I checked, it has the best ZDP (ZDDP? can't remember) percentage per cost. ZDP is an anti scuff additive that used to be in oil made for gas engines, but was mostly eliminated when it was determined to be bad for catalytic converters. Not really true anymore, but it's absence is still the norm. Never a factor in diesel engines, so it is still there. Royal Purple is supposed to be great too, but expensive and I have not used it myself. Rotela has no issues with wet clutches. I rarely see it in quart containers, and since it is usually in 1 or 2-1/2 gallon jugs (trucks) I always have it on hand so it goes in everything. On the other hand, stock engines with proper oil changes mostly last indefinitely with most any decent oil. Keep in mind, the SAE rating on the container is policed in no fashion whatever. You can put water in a bottle and sell it as the most extreme spec, no one will care until their engine blows up. It is only a claim by the seller that it meets the SAE spec, so consider the reputation of the manufacturer.
