I had an arc at all my plugs in my 360 with autolite 64's. I changed them out today to NGK 2023's. At idle it still exist but not always like before. It actually looks like a ring around the plug. Can't tell if it is around the porcelain or at the thread. What are some thoughts and sollutions? The accel yellow wires are at least 10 yrs old. What about using dielectric grease around the threads?