Not sure about your engine... but have you considered that it might be
problem with your belt? Maybe the tensioner too?

Hi, I have found that the best way to remove oxidation from electrical
contacts is via mechanical means.  Chemicals usually won't get to the
good metal necessary for conduction.  A small pocket knife blade
usually works well, sometimes a small peice of scotch brite (name
brand, but other abrasive scouring pads will do) is gentler.  Just a
small suggestion.  Hope this helps.