Most of the time they look like a small rubber o-ring or doughnut.
you can see if its leaking if you have the spark plug in tight and then fill up the spark plug tube with gas and see if it leaks out if it doesn't its still leaking from the top one
They seal oil/water/dirt out of the plug tube.
Twist boot then pull, this will break the seal from the plug.
There is current leak. Find the leak and seal it.
For Hemi heads where the spark plugs are in the top of the head and there is a tube in the valve cover where the tube meets the head is the tube seal. It is basically an O ring.
If I'm not mistaken it sounds like you've blown a water seal! Overheated?
You can try twisting them on the plug to break the seal. Sometimes it is impossible and you need to replace the wires.
replace valve cover gasket. there are 4 small rings that seal the plug ports. this keeps oil out of the spark plug port.
leaking spark plug wires can do it and also a clogged fuel filter. it could have a bad spark plug or a bad spark plug wire a bad coil pack or ecsesive oil leaking past the valve seal and its fouling a plug
Failed seal under the valve cover on top of the plug tube.
spark plug maybe is wet with oil because your valve cover seal is bad.
The seal on the top of the plug tubes are leaking. You need to change the valve cover gasket and plug tube seals.