Wow, that Volcan is a beautiful example of a great Gottlieb game!
I repaired one along time ago. The only "mod" I did to the game,
is that I separated the pop bumpers and put them on their own
relay. It helped tremendously the dreaded ball jam/dead between
the point where the ball hits one pop bumper and bounces into the
other at the same time and does not recache back because the relay
is between moments of activation and resetting.