Have you done the test yourself? How could you possibly measure viscosity of oil at those high temps without lab equipment? Microwaving oil for 30 seconds probably won't raise the temps to engine temps anyway.

I also don't subscribe to "Oil Company" conspiracy theories. What would they gain?

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1970 280SE Coupe W111
Chassis Number: 111 024 12
Engine Number: 130 980 12
Exterior Color: 180 - Silver Grey Metallic
Interior Color: 243 - Leather Light Red
Transmission # 004470