@DMG- a compression test and leak down test can tell you a lot about the health of the engine, in your case I would certainly do both. Steering on a DD is a similar test, look for little rudder to steering wheel free play and a free steering cable (steering should be a one finger amount of effort). Check the rudder to bushing play. Transmission should engage / disengage quietly. The shaft seal will probably drip, that is normal and it should not be more than slightly warm to the touch after running. When test driving note the following - the boat should probably pull slightly to the right or take a small amount of left hand down pressure to follow a straight path, that is normal and when you go to reverse, it will back up to the right, normal for a left hand rotation prop. Drive train should be smooth and vibration free. Good luck! And in case you don't know, that model boat is really well liked by its owners, there are several on this site that love them and tend to be hard to find.