just so there is no confusion in case someone does a search. the GTX specific model does NOT have a nut on top but only the bottom. the post is designed to have a little play. exactly how much im not sure. but the only way to adjust this nut is from underneath at the bottom.
still would be nice to tighten this nut a little. but again im not sure whats all involved in doing so. if i have some time in the future ill take the ski out from the marina, bring it home and work in it.