That old of a ski needs the starter removed, cleaned internally & new brushes. The E-box may have moisture in it too. Suggest you take out
battery, pull floor lever to release the E-box and pull back & up to sit on top of magnito houseing to open, starter relay is in there. Removeing the tuned pipe helps to get to starter, but I've used a mirror & bright light.
Last thing you want is to have your Babe on the back and ski not start and be stuck with noone around!