I was digging around the WEB this evening looking for solution(s) to an issue I'm purusing with one of my Asian vehicles when I stumbled across a site that featured tech tips from professionals. One that I found particularly interesting, especially for MB diyers with M103/M104 motors was a way to determine if a head gasket is blown or leaking. The text from this article has been cut-n-pasted below. Maybe this approach will be of benefit to someone here in the near future.

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Fill It Up: Being fooled by chemical testing/infrared testing of the cooling system for head gasket failure(s), I stumbled on a better method, which is much faster and more accurate, too. Next time, try this:
1. Remove all the spark plugs from the engine.
2. Fill the cooling system right to the rim of the radiator neck.
3. Disable the ignition system.
4. Insert one spark plug in a cylinder and then crank the engine for five to 10 seconds, while watching the radiator level. (A remote starter comes in real handy here.)
5. Repeat step 4 above for all cylinders.
The idea behind this is simple: This uses the engine’s compression to pressurize the combustion chamber and force this pressure past any potential head gasket/cylinder head leakage into the cooling system. Should there be a leak, the level in the radiator will overflow. The reason all other spark plugs are left out is to allow the starter to spin the engine faster, without shaking so much and helps to identify which cylinder is the culprit. Why not let the 150 to 200 psi compression do the testing? Now, 13 to 15 psi in the radiator to test it just doesn’t seem up to the job anymore, does it?
Brad Petersen, Owner, ASE L1 Master Technician
Petersen Automotive, Escondido, CA

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"