i was told 2 days ago by a merc dealer the arm is about $60.00 and about an hour labour to change if you cant do it yourself and you have a jap merc 18 hp super and just to add something to the convo enlighten me if im wrong beside aftermarket mods your usa 15 mercury is and will be a 15hp without squeezing a cheap few extra ponies like the 15 jap merc..