I actually love halletts, and the 500 hp motors..but I'm not the brand loyal guy that won't say about the problems the 500 hp has...they have their problems , but easy fix's IMO.. #1 is the stock carb... they have to stagger jet it to fatten it up, but they still run lean on 5&7...and that where they like to burn through the head gasket.. somewhere in the manifold design there is a problem...next, the valve train, anything past 200 hrs' you are running on a prayer.... now, that all is gonna depend on how the boat was run for sure...running it WOT ...better check it out..I've had 6 of these motors start to come apart at 200 hrs..the roller rockers and lifters should be replaced... in fact... thats one of the requirement from merc...the next is the blind holes on the head bolts...the bolts bottom out and give false torque readings...with 5&7 running lean, they like to cook the valves, they tulip and will suck the valve/break the stem, and bye bye motor...