Hello, I have a 1995 330DA with 7.4L Hurth V-drives with Kohler Genny. I bought the boat last August and had impellars, complete igition tune up and carbs rebuilt. Boat runs solid. I am not handy but I do keep up on all the preventative maintence I can. This Fall when I have my marina winterize is there anything else I need to do besides have them winterize all the water systems, AC, etc, change the oil and filter in both engines and genny? Ive always had outdrives to maintain but now I don't. Do i need to do anything with the Hurth V-drives? How often does the oil need to be changed? Any other yearly stuff I should be doing? PS. I boat in Minnesota on the St. Croix River so no salt! THANKS!