Hi,
Ya, I had that problem too. It is the fiberglass box (aqua lift muffler, I think it's called.) it comes out pretty easy, just 4 screws (one on each corner) The biggest thing about getting it out and back in, is the heavy black muffler hoses. You should be able to get them to back off enough to lift the box out (you will need to loosen the large clamps.)
If you do an inspection on the dock you will find some sort of leak from the box itself, probably along the lower edge (underside.) It's not built very well and prone to a split or crack at the seam or maybe at the screw holes.
My problem was the underside seam. I first tried just some putty like stuff. (liquid steel I think) I just pushed it into the area. It failed after a few months. So the next time, I used the grinder on it to get a clean surface and used a few layers of fiberglass and
epoxy. Now My fixed area is stronger than the rest of the box! The good thing is, it doesn't matter what it looks like when your done.
Good Luck, PM me with any questions, glad to help.
Todd
s/v Hestia
currently: New Smyrna, FL - Bahamas bound!