I'm going to look at a used 2006 yamaha 250 four stroke. They say it has 600 hours on it and the guy replaced it with a new 300hp. Concerned about corrosion as it's my understanding 250 built prior to 2008 could have this issue. The shop wants 6k for the motor. What would you do? Let's say it has good compression and the mid section looks ok... Would you go for it ?