I have an I/O mercruiser, 2.5L, 4 cyl., 120. (Stern drive ser. # 6736684) <br />While running the engine the muff slid off the water intake and ran dry for a minute or two. Now <br />the engine overheats. I'm trying to replace the impeller, but don't know where to find it. Is it better<br />to replace or rebuild the impeller unit?