It could be your glow plugs that are causing the problem. They do wear out over a period of time and need to be replaced. Unfortunately they do not have a maintenance interval and so it is solely dependent on how they are functioning. We do recommend that when you replace your glow plugs to have all of them replaced.
If your diesel engine is having issues starting give us a call at 541-791-2886 or request an appointment online and let us take care of you.