Hello dieselnut14
I hope that I am wrong!!!
I have seen this before and it is not pretty.
The heater is part of the engine cooling system.
#1. The windshield washer heater tube has a hole in it. = replace it.
#2. Clean the windshield washer tank and system with mild soap, flush with at least two full tanks of water, then refill with solvent.
#3. Someone has put domestic green coolant in the car. = full flush and neutralize the system.

A pressure test of the cooling system will show the leak, if you want to confirm the diagnosis.
You can use a piece of steel tube to bypass the heater as a cheap fix, unless she is in Alaska or Main.

__________________
ASE Master Mechanic

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1983 300D

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