I would be heavily scrutinizing the intake to see if there isn't a crack near the thermostat housing or a crack near the brass nipple on the back that the heater hose connects to. These are the two common failure points on the plastic intakes and when they start to leak they'll fill up a spark plug tube and short out the ignition coils in the process.
As for the oil getting into the spark plug tube, I'd examine the valve cover gaskets and see if it looks like oil has been seeping from around the gasket near the spark plug tubes. When I had to change out the intake on my '99 I ended up having to change the valve cover gaskets as well since some of the plug tubes had oil in them.
Hope this helps and let us know what you find.