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” GOD IS GOOD