First off, welcome to the forum.

Second off, you shouldn't put gas into a diesel Mercedes (fuel mileage is the correct term).

As for how fuel is leaking past your cap, like another member said in a similar thread just yesterday, check the rubber gasket on the cap. If it is deteriorated (due to age or using biodiesel) then every time you make a sharp turn to the left fuel sloshes to the right side, surges up the fuel filler tube, and leaks out from under the cap...

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown