I wondered if it might be unleaded fuel, "regular" fuel up until the early 80's had Lead as an anti-knock additive. Similar purpose to the Zinc in oil, it helped smooth irregularities between high friction parts. I hope the additive sorts the issue.EZ, my 2003 Jeep 4.0L six is said to be the same way on zinc. Based on some forum info, I just put a HD 10w30 in it which is good for diesels and gas motors. It seemed to have helped.
Just had another thought, how often do you drive it for more than 30 minutes? Do you ever get it out on the highway? If it sits long periods between uses lubricants settle out, air bleeds from tires, etc. I am sure you know all this, I'm just running some trouble-shooting through my head. I would love to see an image of your "baby".
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