Rest easy...

...an oil gauge pegged to the max indicates a faulty oil pressure sending device...when it goes bad, the needle goes to "3" simply by turning the ignition on...even without starting the engine.

Unless you've suffered catastrophic engine damage recently, your oil pressure is just fine.

I had to replace mine on my W124 last year for the exact same symptom. Since it's a different engine I can't tell you exactly where it's located...but it's goes for around $70 and is about a 15 minute DIY swap.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car