Hi I heard from a guy who had problems with a few year newer one, there is a sensor on the front of some of those motors, down by the crank pulley that can cause problems, it's not the mud was so deep and it's damaged that? only guessing with this but might be a thought?.
If you got 18 month old bio diesel blend in there it probably will look like junk. That stuff don't keep! The fuel bugs love living in there munching on the bio part, and you get black slime in the tank and up the lines plugging stuff up. Regards Robert