I have a 1999 Hunter 380 as well, and just last weekend changed the impeller. What a royal pain in the butt. The previous owner did put in the access panel....and then never changed the impeller in 4 years. After last weekends 4 hours of hell, I know why. I did get it done, thank God since there was only one paddle left. But, what Yanmar was thinking in putting the access where they did is incomprehensible. Some advice: 1) You need needle nose pliers to work the impeller out far enough that the impeller puller (needle nosed pliers with hooks on the end...expensive but worth every penny), can grab it 2) Getting the gasket ring to stay in the groove long enough to put the plate back on is a challenge...finally solved with a lot of sweat, cursing and a bit of silicone 3) unless you have very small hands you will drop the screws several times in the process, followed by more cursing. The good thing is they fall right in the pan and are easily retrieved.......after getting up and walking all the way around to the other side of the engine......several times in my case.
Will I do it again??? Yes, in 2 years not one. Hopefully it will be like labor pains to an expectant Mother. They say they forget the pain or you would never have a second child. In changing the impeller it will take every bit of 2 years for me to forget what I just went through.
Tom