Most minor, single mouth ulcers are caused by damage to the mouth, for example by accidentally biting the inside of your cheek while eating, or from a sharp tooth, food or filling.
I have a 2005 Honda Element. The owners manual states the brake fluid should be replaced every 3 years. When I asked the dealer to replace the brake fluid, they said it was going to cost $190. I told them last time they did it, it was only $27.
Revised by BoatUS editors in April 2012. Engine manufacturers typically recommend an oil change every 100 hours, and at least once a year. Even if your engine manual allows for a longer interval between oil changes, changing the oil more often will extend the life of the engine.