I think you need to remove the outdrive. It's simple. Water in this area sounds like water in you drive shaft bellows. If so it could lead to real problems, if it hasn't already.
To remove the outdrive, place the console shift lever into FWD gear to align the drive's shift coupler. Remove the speedo tube connection from the drive. Remove one plastic end cap, the E ring an washer from the end of the rear trim cylinder rod and push it out. Use a 5/8" socket to remove the six nuts. Pull the drive off.
You should do this annually, at least every two years to inspect things. If you find water in the main drive shaft bellows it needs replacement. Your gimbal bearing and U joints could be compromised from the water.
