my brother's 00 E320 suffered from same ailment for 3 yrs even after visits to
the dealer. when he went to Kabul, I was left to care for the car. one day,
apparently nothing better to do, I pulled out a large Torx bit and loosened the
two fasteners on the door strike. i moved the strike a hair towards the out-
side of the door. it now closes with normal effort.
bear in mind that this adjustment requires a careful balance. the adjustment
to the strike can be made too far/much that the door loses positive contact
with the door switch....which controls the dome light, alarm, door locks, etc.
so keep an eye on strike plate and door switch and balance any tweaks so
that all systems continue to function properly.
i'm not concluding that my fix is suitable for your anomaly. something like this
can be initiated when the door is slammed against an obstruction like the
metal end of a seat belt, or some other.
in the end....just a possible cause/effect for you to consider