I have 2003 Mercury 3 cyl 90hp with oil injection, I have fuel leaking into the attenuator from a small pipe (about 1/8 inch OD) in the bottom of the throat of the middle carburetor, just in front of the throttle valve. I am trying to find out what to do to fix it. Boats.net carries a carburetor repair kit -Mercury Part# 8236354. If I need to dissassemble and remove the carb do you know if this kit containsall the neccessary gaskets and parts?

The repair kit does not include the float.
It is possible to have a bad float.
If your motor is run regularly I would order 1 kit and 1 float.
If your motor has been sitting for a while (over 90 days) and this happened, I would order 3 gasket kits and remove and clean all 3 carbs.