98 neon- weird stuff in spark plug tubes

Hello! I'm new here, but I have a concern with my neon and I was hoping one of you wise ones could help. I have a 98 neon 2.0L DOHC with about 78,000 miles. I started getting a code for a misfire in cylinder 3 and I've had a few really rough starts, which clear up after the car is running for a few minutes. I decided to change the spark plugs and wires. When I pulled the wires out of the plug tubes, I noticed a weird black substance that seemed to have melted and then cooled into a hard goop all over the wires and in the tubes. It doesn't seem to be on the plugs. There's enough in the tubes that I cannot really fit my socket wrench in the tubes to get the plugs out. When I look in the tubes, it seems like the goop is somehow leaking out about halfway down the tube! It's in all four tubes. I don't know what is happening here. I had my head gasket replaced a few years ago. Is it possible they put some type of sealant in there that is now gumming up my plug tubes?? or is this possibly something the mechanic could have messed up when he changed my spark plugs last time? please help! The car still works fine (except for the occasional rough start), but I don't want it to ruin my engine in the future!

Your spark plug tube seals may have corroded and fallen into the plug hole. They are easy to change...all you have to do is remove your valve cover to get to them.

* Mod Statement* I know this post may be old, but I am trying to answer the questions with no replies, to get some useful info out there.