Thank you for the replies. So it looks like the yellow/white powder coming from the valve-stem is water scale and not metal corrosion? So the water is leaking out very slowly and it evaporates before it would get the area wet underneath the valve?
If that's the case, I will try to tighten...
I am hoping to find the best replacement option for a corroding hot water valve on the supply line for the hot water heater tank. I suspect the reason for the corrosion are dissimilar metals reacting to each other (valve and pipe).
The copper line is connected to an old-type plastic...
