I had 1 that leaked like that, here's what I did and it worked.
Attach (or have someone hold) a shop vac to the oil inlet on the valve cover, turn it on.
Spray some brake cleaner around where the leak is to clean the area, only a little bit.
The shop vac will suck air in where the leak is, apply sealant (rtv) to the leaking area.
The vac will draw in the sealer at the point of the leak so that it's not just sealed on the surface. let it dry.
