2002 Lincoln Navigator 5.4L 32V Intech V8

This car has 135k miles. It was giving dtc codes for misfire in cylinder 1. I found it was due to short between coil and plug because there was fluid in the plug well. I just blew the liquid out with compressed air and added grease to the bottom of the coil boot. I found I could do this monthly and avoid misfires. Eventually the problem began occurring in cylinder 2 then 3 now 4, all the cylinders in the passenger side bank. There fluid seems to be coolant. It’s oily, but not sure if that’s from the grease. It appears to be a small amount of fluid that causes the short. I have not had to add coolant to the reservoir. There does not appear to be any coolant leaking from the heater hoses and the previous owner had a heater hose bypass installed presumably due to leaking heater core(s), so I doubt there is even coolant in the heater hoses. There is also a sealed dust cover that goes over the the coil packs and plugs. 

I am not a professional mechanic, but I did successfully perform intake manifold swap on my 03 f150 with the 5.4, but that engine had the plastic manifold and it was a common failure that would lead to cylinder 1 misfire. I cannot find much information that the manifold is faulty on the intech and I’m hoping it’s just the gaskets. 

My question is whether this is likely caused by intake manifold gasket failure or if it more indicative of warped or cracked head or head gasket failure? Can leaking intake manifold gasket cause fluid to accumulate in spark plug wells?

I would rather just keep blowing it out periodically than spend a day tearing it down only to learn I have a warped/cracked head or head gasket problem. 

Sorry if this is a redundant question, but I searched the forum and could not find this specific issue. Love the videos!

Thanks in advance.