Cylinder 3 misfire revisited

All,

On my ongoing saga of locating why my check engine light keeps posting the
code of 0303, I noticed more coolant being used. The mechanic did a
compression check and he did say that it was normal. But he was concerned
that my intake may be leaking causing my coolant to leak into cylinder 3.
The noticeable symptoms the engine displays, is a slightly rough idle when
first started. This was fixed when mechanic changed plug and plug wire, but
has since returned. Also, my coolant has dropped a little. And if the CEL
is cleared, it does come back with the same code of 0303.
I have not pulled the plug in cylinder 3 to see if it is a noticeable color
difference compared to the rest. Would the engine show any other symptoms
if it was a intake leak? What about if it was a head gasket issue.
Explorer is a 1999 XLS 4.0 with 106,XXX miles on it.

Thanks for any input.