While you have the plug boot off the wire, use a volt / ohm meter to check the resistance in the boot.
There is a resister in the boot. The resistance should be in the neighborhood of 10K ohms.
If significantly different look into the spark plug end and see a screwdriver slotted retainer.
Unscrew that and a spring and the resistor will come out.
Clean up all the contact surfaces and the inside of the boot, then reassemble and check resistance again.
If you find that boot out of spec, it might be worth checking the others.
After 7 years, don't get in such a hurry that resurrection may be delayed further by damaging anything unnecessarily.
Be patient, don't lose focus and don't throw anything, you'll get there.
dan