I have run the same boat with a 1999 Ox66 200HP for the last four seasons and have probably put over 550 hours on it. I haven't had any problems, but I have been very aggressively performing preventative maintenance. I think the general consensus is that these are very reliable motors, a little gas/oil thirsty compared to DFI and 4-strokes, and require some basic maintenance to keep running well. When I was looking at my boat, I did quite a bit of searching to see if there were certain model years to avoid, common problems, etc.. and didn't find anything. Just like purchasing any other used engine/car/boat, make sure you ask some questions to get a feel for how well they took care of it and whether they did the maintenance themselves, took it to a mechanic, or just neglected it.
Here are some items that you can ask to feel them out:
If the boat has been running Ethanol (E-10) fuel, ask how they made the switch from the older MTBE fuel.
When was the last time you changed the low pressure fuel pumps?
Has the oxygen density sensor ever been inspected/tested?
Has the VST filter ever been inspected/cleaned?
When was the last time the water pump/impeller was changed?
-- Tom
