The manufacturer recommended ambiguously, the point of this thread. Additionally 1 of the 2 possible recommendations, 20w40, isn’t available anymore.
About the same as it did new. I have a strong magnet. I put it on the bottom of the draining tub. It didn’t attract anything. At 2,583 miles in a well-maintained engine I expected no different.
I won’t. This oil looked okay. My engine sounds the same as always. It has spec compression. It gets NHTSA gas mileage. I pass biennial emissions tests with numbers as low as those required of new cars.