Had mine rebuilt a few years ago. One year out of warranty and fried a cylinder. Posted on CF and found a guy in charleston that rebuilt it for half the cost of all other bids...one man shop. Builds and races 2.5 Mercs, the ones that sounds like an Indy car. I'll look for his info but it may be gone. Motor runs better now than it did new.
Chris at http://teamcharlestonmarine.com/ did a rebuild on a Yamaha F150 for me about 6 months ago, and I would recommend them. (I presume they also handle Mercs, but not sure.)
In my case it was difficult finding the recent model parts in a hurry, and that was the closest I could find ready to go. But beyond that, Chris and his team provided outstanding customer service and competitive pricing.
If you're looking for someone locally in Bluffton, I might recommend Chris at Carolina Marine & Machine 843-837-8800 who we've worked with for several years.