Nissan Repair: Spark plug not fitting, nissan sentra, heli coil

Question
I have a 2002 Nissan Sentra 1.8L engine.   I developed rough idle around 200,000 miles so I decided to have Auto Zone check it once the check engine light came on.  It was showing misfire at #4 cylinder.   I was installing a new set of plugs when I found the #4 and #2 cylinder plugs had been installed too tight or became that way over time.   I was able to get #2 out and the new one in.   There is a red ring around the top of the spark plug wall at the top of the plug to show how far the plug sits in the top of the cylinder.   The #4 plug would not go down far enough or to the same height as the others.  Do you think the threads are beyond repair or is there a tool I can get to use on the threads in order to allow the plug to go down to the proper seating?   I used an old plug to try and help the threads but it broke off and I had to get it out before installing the new plug.   Don't know why these plug threads will not allow the plug to seat properly?

Answer
William,

You better try an anti-seize paste and run the plug out and back again.  Otherwise, you are going to be pulling the head.  If you try the Heli-Coil route, and you could try, it is a matter of cutting new threads and installing the insert.  Then, the plugs go back in with the insert making the new threads.  Problem is, the sutting of new threads introduces aluminum shavings into the cylinder.  People use grease to catch the shavings.  So, you might get lucky and give it a try if using the anti-seize paste and running the plug back and forth does not work.  Otherwise, it is off with the head and a valve job while you are getting the thread inserts installed.