95 E300D, found this UK site while searching for parts
 

Might be a good source for parts that are not that readily found. The example is for a new expansion tank. The Bugiad brand looks interesting and is a German located company.

Checked on shipping by chat and they estimated $100 for up to about 50 pounds of weight, via DHL.

https://www.autodoc.co.uk/car-parts/expansion-tank-engine-coolant-10212/mercedes-benz/e-class/e-class-w124/461-e-300-d-124-131