Upon further inspection, it looks like the leak was caused by an improperly placed clamp on the short 3" tube from the expansion tank to the elbow on top of the head.
I saw seepage, but it really looked like the leak was coming from the elbow/flange. When I wiggled the small 3 inch long hose, it popped off! The clamp had been installed on the wrong side of the bulge, basically it was only clamping tubing, and so finally the tubing slipped down and almost off.
A new piece of tubing was installed, and now I have to fill the cooling system, and run the plane up, check for anything funny, but I think the problem is licked!
Afterwards I did a CLOSE inspection of ALL the other hoses, and it seems that whoever built the engine was not too particular about clamp placement, as long as it was behind the bulge in the metal tubing.
IMO the clamp should be JUST behind the bulge, or maybe a couple millimeters behind it. I found the clamps were ranging from there, to an inch behind the bulge, no consistency.
Anyways, none of those other hoses are leaking so I left all alone, thanked my lucky stars that my leak was a simple, easy fix.
I'm off to refill my cooling system, run my plane up to confirm no leakage, and then wrestle the cowling back on hopefully without scratching my nice paint.
I hope Murphy stays away from me for a while now. I've got lessons to take!
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