Wow, I guess I'm the only one with bad luck. Bought a boat that had only been sitting in a garage, don't know how long. Had it surveyed and paid a mechanic to run a compression check, found out later he only checked a couple cylinders. Couple of the bores were so rusted the rings wouldn't seal. turned over and ran ok, just got a lot of blow by through the breathers. Had to bore it out to clean up the cylinders. I recommend doing a compression test at the very least and if you can do a leak down.

I'd throw some fresh impellers in it too. Those could incinerate quickly while you are looking around at other things asked cause a mess....

Run a bottle of a good "stop leak" and a quart of Lucas Oil Treatment in your oil. I use a qt of Lucas in every oil change and the stop leak will plump those gaskets back up that have been sitting around and drying out (crank seals most of all).

If you are located in an area that frequently gets below freezing temps I would be skeptical. Before you buy bring a mirror and a flashlight and check around the block for any large cracks. Sitting for that long I would imagine if it was bad you might be able to see it.