I thought I would share my story about an episode I had recently. We travelled from homeport about 30 miles to our destination (another marina) without incident. When we were ready to leave the next morning we fueled up, and had difficulty starting the stbd engine. When it finally started it was vibrating and running rough. Upon getting out of the harbor, we could not get stbd engine over 500 rpms, and serious rough vibration. When I checked the engine compartment there was steam, exhaust gas and water spewing everywhere. Shut down the stbd engine, turned on the exhaust blower and returned to the marina we just left under the port engine alone. When the local mechanic diagnosed the problem, this is what he found: dirty spark plugs on the stbd engine caused the excessive vibration, which caused the stuffing box to leak and the port engine exhaust to come loose. Hence, the steam, water and exhaust gas. So, if you haven't checked your spark plugs in forever, you might want to.