First time i ever have used quicksilver quickleen! Just decided to run some fuel system cleaner through the motor, no reason to, was just told it was good to do it from time to time. Well, dont know if its a coincidence or if this product possibly caused this to happened...Lost the #6 cylinder in my 05' Optimax. I use the blue stabil every fill up. Motor has less than 250hrs on it. Do i rebuild or get a new head? Kind of at a loss right now, frustrating to say the least.

225Hp

Did you do the diagnostic and decide the #6 was gone or a mechanic? Could be several other reasons for a cylinder to die in an Opti., thermostate for that cylinder, plug. They are so precise that relative minor things can create problems.

I highly doubt quickleen caused Your failure

There are several scenarios that cause the motor to pop you can normally tell what happened when you have it tore down and have #6 piston in your hand

Sometimes #6 will go due to a cold seizure not as common this time of year as in the winter. But it is from not letting the motor come to operating temp before hammering on it and that blast of cold water comming strait off the water Pump hitting #6 and the aluminum piston swelles faster than a steel sleeve.

Boat was idling for a solid 5+ min before i got on plane, was running about 4000rpm when it went out. Wasn't hammering on it. Ran about 20 seconds on plane before it died... Put quickleen in friday, ran sat no prob, and boom on sunday morning first thing.

Mechanic did diagnostic...

Buy a reman. powerhead from Mercury. Comes with one year warranty and you can buy extended if you like.