I have been experiencing the same exact problem with my '99 E-320. I fill up all the way (I know its all the way because the gas pump stops itself and I keep trying to pump more gas in; 3 - 4 stops).
I am wondering if it is the same exact issue. Let us know if you get it fixed by changing or cleaning the fuel sensing unit.
I would be interested in knowing how it is done and what materials are needed to do it.