Yes you can do it yourself. My guess is that they didn't replace the wiper and the seal. I worked on same thing early this year and had to get seals for this unit from Mercury dealer. Get your model # and serial # and call a local Merc dealer. I know Boats.net doesn`t have the seals.
“The world will not be destroyed by those who do evil, but by those who watch them without doing anything” Remember what He has done and remember that He is not done yet! GOD IS GOOD