I agree with NightWing, water pump is a likely culprit.
Exhaust is not a likely culprit, ignore it for now.
Look at the power steering cooler, fuel cooler (if equipped) and oil cooler too.
I highly recommend pulling the drive to check the U-Joint bellows. It's very easy to do. See:
http://www.wikihow.com/Remove-Your-M...One-Sterndrive You do not want water getting in there, it will mess up your gimbal bearing and U joints.