Aux pump is there strictly to maintain flow in the core while at idle.
Euro cars may or may not have the aux pump, it's not std in the home country.

Many fail and owner's do not even realize that they are not functioning.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles