Recently purchased a 560sel with 34k miles, original southern CA car & spent last few years in southern NM. Car had been in storage & not running for a couple years.
So far, I’ve replaced oil & filter, plugs, wires, cap, rotor, battery, fuses, fuel pump relay, tank screen, fuel pumps (2), fuel filter, accumulator, hoses, air filter & breather element. Car starts & idles beautifully and will drive approximately one mile before stalling quietly without warning. After sitting 1-2 minutes, starts up without hesitation. Stalling continues with shorter intervals. While idling, I looked under car to inspect fuel pumps & noticed a very loud buzzing sound, perhaps fuel starvation or blockage. Needing some assistance with diagnosis or a baseline to get sorted. Thanks in advance.

Buzzing could be a check valve at the pump/filter. Try opening the fuel tank cap to see if anything changes. Check fuel pressure to see what it does just before stalling.

Not sure if this is possible; but, could one the fuel pumps wires have been reversed during install? Probably wouldn't start if so but worth a look.

Good luck!!!

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There indeed may be another cause, but the symptom will be caused by an absence of tank venting.

Thank you for the suggestions. After purchase, I did replace cheap, corroded gas cap with new metal MB cap and it could very well be a vapor lock issue. I’ll remove cap & follow up with any results.