I searched the site and found a few good ideas about discovering slow coolant leaks, but I thought I would describe my symptoms and someone might suggest a direction to explore.

Cooling system history:

New radiator in 7/00 (installed by MB dealer)
New thermostat 12/00 (installed myself)

Leaking history:

In late August coolant level light comes on for first time (cool night drive to Boston).
Over the next four months (4kmi) I've added 1 gal of MB coolant and 1 gal of clean water aiming for 50% mix.
I believe that I've seen fluids leaking, but not while I was watching for them. Some ran off the under pan when I jacked up the car to change to snow tires.

Other things:

This month (12/01) I've smelled a strange odor from the heating system. This seemed to happen when I was stopped on a steep decline.
The dashboard gurgles loudly (but I don't believe this is new), but I learned from the diesel mailing list archives that this is a "feature" of the W124 heating system.
The system maintains pressure even after sitting over night.

Thanks,

__________________
-Mike
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi