I have a Kohler 20 hp. (M20S) and need to change the oil. This will be it's 11th season of mowing and it has 400 hrs on it. I want to switch over to synthetic oil instead of the regular dino oil but I'm not sure I can. I happened to notice in my owner's manual that Kohler recommends 30W oil. I haven't been able to locate 30W oil that is synthetic in my area and other said I could use 10W30. Can I safely switch my engine to use synthetic 10W30 oil without any issues? Also if I'm able to switch can I increase the change interval of the oil and filter. I currently do it every 25 to 50 hours, and if I can increase it, what would be a safe time frame? I did a search on this forum, but couldn't really find any definitive answers related to my specific question. Thank you.