your submarine,
if you have an auto, it is probably a 998, or 999. the vent for this trans is at about 12 oclock just above the front pump behind the torque converter. the height is about the same as where the bellhousing flares with the casing. if you go above the top of the main casing in water, you will get water in the trans. you can modify and plug the current vent, and move it up. of course you have to pull the trans.
regards
ws