Oil In Spark Plug Well & Green Coolant Around Thermostat

Unless your head is cracked the oil has likely came from a leak cam cover gasket or spillage from filling/adding oil (somehow).

The t-stat leak just a bad gasket (o-ring) on the t-stat. Your intake will have the aluminum crossover but it's still possible for those to crack, warp or just break over time. Inspect and replace what ever is needed. Pulling the heads is not needed (at this point).

My 2004 gt has the aluminum crossover, and it was leaking coolant around the thermostat housing area. I removed the thermostat to inspect and I found that under the thermostat where the aluminum and plastic manifold meet, a section had deteriorated and caused it to leak, I glued it up for a temp fix and the gasket that mates the aluminum part to the plastic started leaking after a few months prior to jb welding.

Long story short inspect everything when thermostat is out!

I JUST finished doing nearly the same job on a 2002 Town car with a PI Romeo. There were several coolant leaks but mainly around #4 and #5. I took the intake off planning to just replace the cylinder head to manifold gasket. What I found was in some locations that I knew were leaking the gasket was fine.

After some research I found there is a gasket between the manifold coolant cross over and the plastic intake. Further it is replaceable.

Check out Felpro 35958 for an example. Note, it's hard to find this part because many web sites state it does not fit.

http://www.oreillyauto.com/site/c/detail/FEL0/35958/01378.oap

I'm so glad I found this because it was obvious upon disassembly that this was the true location of the coolant leak.

Regarding oil in the spark plug wells. Two likely sources. Leaking valve cover gasket or under torqued spark plug. In the case of the under torqued spark plug, don't ignore this as it can "blow out" damaging the threads.