I own a 1992 Ford Crown Victoria with the 4.6-liter V8 engine. It now has a coolant leak that my mechanics can't figure out. Originally they said it was a plug in the rear of the engine block so they removed the transmission to fix it, but they found that the leak is coming through an open passage near the top of the engine.
They're now telling me that it's guess work and could be the intake, heads or possibly a crack in the engine block itself. Right now they are ordering a very expensive intake manifold.
Replacement of the intake manifold is a premature decision, unless it was a known common failure to this particular engine, which it's not. Yes, the intake manifold, cylinder heads, engine block and related gaskets are all feasible possibilities for the coolant leak which you have described.
Very often the detailed technical aspects to any vehicle are best known only by the technicians at the dealership who specialize in that particular make of car. This comes into play in your situation.
While your mechanics are ordering an expensive intake manifold, an experienced Ford technician would tell you right away that the coolant hoses under the intake manifold are leaking. That's the common cause of a coolant leak draining out of that passage in the back of the engine block.
It will involve the removal of the intake manifold and replacement of the hoses, clamps and the intake gaskets. The removal of the transmission was unnecessary, but it was a reasonable attempt at diagnosing the problem. Don't be too hard on your mechanics. I'm sure they were doing their best to repair the problem.