Gil, recommend trying a salvage yard or your local MB dealer for a replacement heat exchanger.

Time to consider switching mechanics if the head gasket replacement was unnecessary. Finding an indy with excellent diagnostic skills and intimately familiar/trained to work on MB automobiles can be difficult.

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Fred Hoelzle

We are just going to remove the heat exchanger and make a blanking plate for the cover.
A new heat exchanger is going to be expensive and does this motor really need it?

I suspect it is more of a oil heater in cold climates.