I am not sure what engine (LTR?) you have, but there are likely two thick walled, approx 3/4 inch in diameter, black hoses coming from the transmission to a metal tube that is in the fresh water intake circuit. A large diameter water line will then be going in and out of this large tube. This tube is your transmission cooler. it is nothing but a mini radiator and if it has rotted on the inside, it is pushing water into your transmission instead of just cooling the circulating oil. The fluid level in the transmission therefore rises and begins to leak out the vent into your bilge.
Make sure to change the transmission oil ASAP. I would change, drain, and change again. Then replace the transmission cooler (SkiDim perhaps?). Again, yours may be different. Your manual may show the transmission cooler, as the strainer which MC recommend you clean before each outing (which I believe almost no one does) is located at the bottom of the transmission cooler.
2008 X star, 2005 X2