My 1999 Mercury 150 HP outboard threw a connecting rod last week. Motor always ran great, had only about 550 hours on it. No oil alarm (alarm in working order); not overheated at time of seizure. Running about 4000 rpm. Toying with the idea of purchasing a rebuilt powerhead from one of the larger well-known outfits on the internet and carefully transferring old parts to new. The problem is : not knowing what caused the event in the first place, I don't want it to happen to new motor. Besides oil injection (which I will eliminate by manual mixing), and leaned-out carbs (which I will get rebuilt), are there any other causes other than "bad luck" that I need to worry about ?