I thought I had a head gasket leak at the passenger side rear corner based on the grime there.

It was a hunch but it turned out it was just a dirt/water mixture that had dried leaving some dust behind.

Then, I thought I had located it when I saw fluid on the passenger side heater hose(between the engine and the airbox compartment).

I bought some new heater hose and crawled underneath to get a closer look.

There had been coolant running down the hose for quite a while for sure but the trail started way above it.

I then notice that it led to a bolt that holds a bracket that is attached to the steel heater line that leads from the engine near the elbow.

It turns out the bolt was loose and that there was supposed to be another bolt holding the bracket on but that bolt was missing.

The missing one attaches away from the engine block but I don't recall exactly where as I type this.

I took the the existing bolt out and it looked like it had been in the presence of water/coolant for some time.

It had some crust and rust all long the threads. The rust was just on the surface though.

I tightened the one bolt I had and I can see no leakage today after driving about 200 miles.

The bolt attaches aft of the thermostat housing but not directly to it.

It looks like it bolts to the same part that the t-stat housing does.

What is it and why on earth would coolant leak from there?

The bolt looked like it had an aluminum crush washer between the bolt head and the bracket.

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1993 W124 300D
-297K on the clock as I type this.