I bought my first boat last spring with 220 hours. I changed the oil at the end of the season and put synthetic blend from WM not paying to much attention to its kind since purpose of it was only to keep the boat through the winter storage. I'm about to change the oil before the beginning of the season and got a problem deciding if I should go with regular or synthetic. I know that recommendations are to use the same oil throughout the entire engine live but I don't have a clue what kind of oil was used previously. Now boat got 300 hours and its 2002 maxim 2500 with I/O 5.7 merc. Thanks in advance.