Mobil had a problem with mobil one turning to sludge when used with premium unleaded fuel.
Here in Australia Mobil ran a campaign with mercedes benz during which they changed oil and filters for free just in case the problem had started ot occur in a given car. I think it only affected M111 motors too. That looks like a M111head to me.

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Andrew
300e 294,000mi
380sel 185,998mi
380se 309,980mi