Not sure when the water pump impeller was last changed on my 89 5.7L Mercruiser w Alpha 1 outdrive, so I'd feel better replacing it. Having never done this on an I/O, need any tips you guys may have. The marina mechanic says rather than just removing the lower unit, they remove the whole outdrive. Why in the world would they do that??? Also, the two nuts fastening the front of the lower unit look like a closed end wrench won't get in there. Is there a special wrench made for this? Any advice is greatly appreciated. I have a shop manual and heat for stubborn bolts/nuts. Thanks!