Since it's a new boat, I really like Steves' silicone solution. I've done a number of repairs and relating the problems and fixes needed, most owners decided to 'let it ride'.
You see, sooner or later, most people start over tightening the plug. Too much torque tightening means too much torque removing. Sooner or later, it breaks the bond with the fiberglass and that big brass washer starts turning which in turn starts moving those 3 little screws holding the brass washer. This is the start of the water intrusion that eventually destroys the transom.
Actually, I've never bought a new boat but the very first thing I do on my 'new' boat is rework/replace that garboard drain. I drill out the threads of the brass washer to 1" and silver solder a 1" brass drain tube to the washer. There is usually more work to fix rotted wood but in the end, I use a 'bottle stopper' type plug which needs no torque to tighten.