Hello I have a 1987 Four Winns 170 Horizon with 165 hp 4cly 3.7 I wanted to know what type of non - mercruser oil I can use in this motor ? can I use shell Rotella 15w 40 ? can't remember if it askes for mercruser 25w 40 or 20w 40 ? but would like to use different oil ? but I want to make sure its safe to use