1994 C320. Persistent water in the bilge (if you can call THAT a bilge

)
APPEARS to be coming from the muffler box which is located in the aft cabin.
This boat is new to our club and I've not had experience w/ this type of muffler setup. I "assume" there is is a gasket that may not be seated properly. Has anyone else had leakage like this? And is it "possible" that water is entering the exhaust port on the hull and running down into the box and then leaking.
Any suggestions?
Also, any C320 owners... what hose to YOU pop off to pump antifreeze in to winterize the system?