I'm not sure if Supra changed the propeller shaft seal between your model boat and mine. My boat, a 2007 Supra, has water coming off of the engine and fills the seal / cover around the shaft. Next time you are on the lake, stop and remove the back seat so you can see the transmission and V-drive. Kick everybody off the boat, and turn the stereo off, and listen / feel for water. Mine had 4 hose clamps and all 4 had failed. At that rate it took about 45 min to an hour before the bilge would come on, but it ran for about 5 min to empty the bilge. After replacing the clamps, no more water running in, or bilge coming on. Because of the design of the system, I still have water in the bilge after a day at the lake, but it drains in a couple of minutes from pulling the rear plug. I hope that helps, as my dealer could never find the leak...it took me listening and feeling for it to find it.
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2007 Supra 24 SSV 340 CAT
Lake Bryan, TX