You know people are trying to help you out----if you don't want help or suggestions from people who have been working on FE engines since 1958-----
Now , if you would like to consider a few facts-----
oil condensation, whatever the source will appear IF the
oil is up to temp and is not properly vented
Oil temps are effected by systems with over capicity, coolers not needed or too large, improper oil ( Mobil One ), improper water temps, short trips
Most of the manifold gasket problems are installer self induced---if your manifold leaks or the gaskets leak--go look in the mirror and you will find the person who had the last chance of preventing the leak
So, I am assuming from your posts that you took the manifold off the engine and have now reinstalled it to pressure test it????
I repeat that your Valve Cover CONDENSATION is because of poor vent system and too cold of oil temperature no matter if your neighbor poured the water into the pan
Thats the way things work on internal combustion engines whether they are FE are model T