Hi again Ken,
Very possibly the issue you have is caused by a localized area of the paint being slightly porous and
the wood underneath being slightly resin starved.
A little water gets through the paint and the wood soaks it up, causing a tiny crack.
It's not structural, and once you seal it you should have no more isses.
Better, I think, to use the hald round riffler to file out the crack so you know you've stopped it, then
seal it up and paint it.
You could simply seal the crack, but you would never know to what depth it leads and if it would cause
some issues down the road if the paint leaks again.