A sterndrive needs holes through the transom at or below the waterline: for the drive shaft, the shift cable and the exhaust. BoatUS points out that the only thing keeping the sea out is the rubber bellows clamped over each, where they're hard to see. After hurricanes, it says, bellows failures are the second biggest cause of boats sinking at the dock.
What a surveyor checks
With the boat out, move the drive port, starboard, up and down to see as much of each bellows as you can. BoatUS's list is cracking, brittle rubber, rust showing on the bellows and corrosion on the stainless clamps. Barnacles and shells can slice the rubber, so growth has to go. Inside, look for water tracks at the transom and a bilge pump that cycles at the berth. Ask for the date of the last replacement.
In the report
"Sterndrive, drive shaft bellows cracked at two folds with rust showing, clamps corroded. No record of replacement. Replace all bellows and clamps before launch." See sterndrive bellows.