The engine exhaust exits the boat through a hole in the hull at the stern just above the waterline. It should be watertight for two reasons. One to stop exhaust fumes getting into the boat and gassing you and two to stop the boat from sinking!
I had noticed some time ago that the rubber of the exhaust skin fitting was cracked. It is pretty old. When I asked a Vetus rep (the manufacturer) at the Southampton Boat Show last year he suggested I should examine the fitting more closely.
I am glad I did as the crack on the outside hid a totally failed fixture. The exhaust inside the boat covered the cracked fitting so it looked fine until separated. The picture says it all.