Thread: WHAT CAUSED THIS?

Thanks thill

That 'seal' is known as a slinger. It's purpose is to keep grit away from where the driveshaft enters the pump housing. It rides just above the housing, not in it. I know of no mercury special tool designed for it's installation but using the guide tube does make it abit easier. It's not uncommon for them to migrate up the shaft. Backing off the throttle quickly or 'blipping' the throttle repeatedly will cause it. Among other things. No real concern to have since you are pro actively keeping up with maintenance.
Over pressurizing the cooling system with muffs is all but impossible and there's good reason not to be concerned. The muffs will spread and relieve system pressure if delivery pressure exceeds pump demand. But if pump demand exceeds delivery pressure, the pump will either draw air or create cavitation bubbles. Either of which can damage the impeller. Since positive water pressure is being fed to the cooling system, muffs should not be used to gauge the health of the pump.
The residue on the pump body is of no concern. It being blotchy tells me it's of an oil/water nature. Most likely residue of unburnt two stroke oil that has mixed with contaminates of lake water. If wiped, it should have an oily-grity feel.