For anyone with the dreaded leak on either a Corsa or Combo, go out and buy a tube of silicon/panel bond, SEAL the servo. You wont see where its cracked, pouring water over it wont solve anything, the water doesnt flood through like niagra falls it slowly seeps through the tiny cracks that you cant see in the seal. As already said this is very common on Corsas and Combos, save yourself the money of garage diagnosis and do it yourself.