Here's my 1 cent worth: from what I've read, today's oil in general have a very much reduced zinc content. Studies found that Zinc causes degradation, then failure of the catalytic converters in modern vehicles. So, the EPA stepped in & mandated the gradual reduction of Zinc in modern oil formulations. The Ural, like old school bikes, have flat tappets & zinc provides lubrication properties to the metal to metal contact. ZDDP additives are sold mostly to hot rod enthusiasts...yep, they're still around. Yeah...back in the old days before the EPA, automotive oil was used in motorcycles cuz like most cars of yesteryears they had flat tappets. We were also not as conscious about the environment as the majority of us are today. I started adding ZDDP to the dyno-mix oil I used & quieted the engine some & seem to run cooler...power of suggestion...maybe??? I currently use synthetic oil (20w/50) with high Zinc contents. It was developed for the hot rod enthusiasts of today. My Ural is just happily humming along.