Take the plug caps off the plugs, pull off the plug caps. Cut a half inch off the ends of the leads, now with the boots rolled back screw the leads back on the cap. Fill the top of the plug cap around the lead with vaseline, push the boots back on. Put the caps back on the plugs As long as there is no corrosion in the cap that should sort it.
Did it to mine a few years ago, never had a problem since.
Did it to mine a few years ago, never had a problem since.