After the summer trip at alpenchapter.com I decided to bring my radiator to a company for minor repair (it was leaking a very little bit right between the mesh and upper hose connection. The company re-soldered the brass inlet )it is a 1916 brass radiator, but they notified me about 2-3 very small holes somewhere in the mesh. Some very tiny air bubbles came out when air pressure of 0.3 bar was applied. They wanted to sell me a new mesh
I decided to let it be as is and to see if I loose water at all (because the cooling system normally has no pressure at all).
Well, last weekend the radiator was reinstalled, filled with plain water, and I took a ride, too. Everything fine, the company must also have done some cleaning, it is cooling a little bit better than before. (Perhaps therefore this microscopic holes now in radiator tubes?)
Today I had a look if the radiator is leaking and saw some water drops under my Lizzy on garage floor, but they were at a place where water from radiator cannot get to. The droplets were below the front end of the engine block on right side. I started searching, but the radiator appeared absolutely dry. I placed now some kitchen paper between crank and bottom of radiator. When the radiator is leaking, I will see this on the paper tomorrow.
After 15 minutes I had a look on that. I saw new drops on the floor, so I continued searching. Good news, the kitchen paper below the radiator is still dry.
Bad news: I found some little puddles between oilpan bolts, right below the metal plug (see picture). (Btw.: The copper part in foreground on left side is my oil can. It found a good place there.)
Fifteen minutes after wiping everything dry and attaching a sheet of toilet paper as indicator, I saw that 1-2 drops must have soaked into the paper. Another drop was hanging on the front of the metal plug, when I touched the plug, my fingertip was wet. Seems my Lizzy will get a new name, "Incontinentia"...

Is there a simple way to seal this leakage?
My first idea was to clean the plug as good as possible with brake cleaner spray and other solvents from any dirt, paint and oil, then apply some glue or sealing goop I used to seal the oilpan and hogshead when I replaced the clutch. But this is relatively close to the manifold, so the temperatures there could be a bit to high for this method. Or will it work? I don't want to make it even worse.
Any useful suggestion is welcome.
Thanks in advance!