My guess, bad water pump seal.
All you gotta do is pop the water pump, take it apart, replace the seals and put it back together again. Honestly, there really isn't anything else it could be, thats the only spot where the water and the cases join anywhere near the gearbox.
I got this from another forum, but it's pretty good info:
First, get it mounted in a padded vice, not too tight.
Loosen and remove the center bolt, and CAREFULLY wiggle the impeller off the shaft. It’s fiber-plastic, so DON’T be tempted to pry it off with a screwdriver!
Here’s the pieces-parts disassembled.
With the housing mounted back in the padded vice, the next step is to use a screwdriver or punch to lever out the rubber seal.
Once you get the seal out, clean up the housing, and the water pump shaft ends. Take a look at the shaft, and if it’s grooved, it’s time for a replacement. Take a look at the bearing too. Are they smooth and silent running like mine, or are they rough and noisy. If rough and noisy, it’s time to replace these too!
When everything is cleaned up, grease the inside of the housing, and the outside of the new seal. Get it started square with the bore, and drive it home.
Grease the shaft, and slide it in from the back side.