[200q20v] Reluctant Spark Plugs

[Forhan, Thomas]

I started to pull the old plugs before work today, and they come out very
slowly. At first I thought they were stripped, but there was gradual
movement and  when I got two out it turns out they are covered with a
varnish like substance from the threads up onto the insulator. My first
guess is that they actually were not tight and what I am looking at is
residue from years and years of minor leakage from the combustion chamber.

My real worry is putting the new plugs back in, 'cause this deposit must be
on the threads in the head as well. As sticky as they are, it seems like I
would not be able to tell the difference between the stickyness and
cross-threading.  Should I try to clean them a bit with some sort of
solvent, like Liquid Wrench? I'd rather not take off the valve cover, and I
sure don't want to run a tap down there!

Thanks

Tom F.