On a saildrive, the engine and the drive leg are one unit. The leg drops through a big opening in the hull, and a heavy rubber diaphragm seals it, carries the leg's weight and isolates the engine's vibration from the hull. With no separate shaft there's no shaft alignment to get wrong, and no cutless bearing to wear.
The catch is that one piece of rubber keeps the sea out. Volvo Penta recommends replacing the diaphragm every seven years, as Dick McClary reports on Sailboat Cruising. Yanmar typically uses a double diaphragm with a water sensor between the two seals, which sounds an alarm if the outer one is breached.
What a surveyor checks
The diaphragm's age from the boat's records, against the maker's interval. The seal and its clamping ring inside the boat: McClary notes the steel ring can corrode where water sits against it. Outside, the leg's paint and anode. The gear oil, for any sign of water past the lower leg seals.
In the report
"Saildrive diaphragm, no record of replacement, boat's records show the original seal. Replace to the maker's interval at the next haul-out." Give the age and the evidence for it, because the insurer may ask.