Figure out where the leak is, and proceed from there. Wash down the trans with some soapy water and a brush (not a pressure washer), rinse it off, drain the bilge and let everything dry. Put some newspaper in the bilge under the transmission ( or a white sheet, or some paper towels), drop the boat in the water, run it for two minutes and see where the ATF is dripping. It might be a hose going to the cooler, it might be a front or rear seal. Once you know, the fix will be a lot more obvious.
1998 Maristar 200VRS