I have a question . . .
Is the coolant passage on your engine mounted to the intake manifold, or to the cylinder heads?
Even some of the older Ford modular V8 engines had an aluminum crossover mounted to the plastic intake manifold. If you have this version, the manifold may be on the way out.
Updated . . .
I just looked at Rockauto, and you apparently do have the type of manifold I described
It is my opinion that your intake’s days are numbered. I’ve replaced enough of that kind of manifold to know the warning signs . . . oil and coolant in #1 and #5 spark plug holes
I advise you to get the genuine Ford replacement, not the Dorman product. The Dorman intake will only work with Dorman gaskets. And that might be a problem down the road. Not to mention that Dorman parts seem to be cheap Chinese parts. I have nothing against Chinese people or parts, as long as they’re high quality.