When I first got my boat the water tube on my Speedo would blow off and spray water right in my crotch, Seems it only happend on the way back in to a weigh-in. Pretty enbaressing! My partner would have to go to the scales and I would just hang out by the boat putting stuff up. Sounds like the same thing with your WP gauge. It should just a compression fitting, Just make sure the hose is in all the way and tighten it up. I know they should take care of that but ain't worth the effort to take it back for just that but since there's other problems then make them fix it!
Cain't help ya' with the Yamaha stuff though