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Why do we care about zinc with a roller cam ???



Roller followers don't care about zinc but the gears may benefit. 15W40 sounds like diesel oil so it probably has a good amount of zinc in any case.

I'm no expert but that gear looks pretty worn... I'd replace it.

Agree its a good idea to re-examine the HP pump and maybe oil. What are oil pressures running (hot idle and hot at speed)? The HP pump doesn't help at idle and may not be needed at speed. If you have more than 20 psi at idle I'd definitely try a thinner oil. Even lower idle pressure may be OK if it doesn't spend a lot of time there (race application).