From my experience, overhaul is not in the vocabulary. The blades can all be replaced/sharpened. Some people keep two sets of blades so one can be in use and the other sharpened and ready to use. I've found the blades stay sharp remarkably long, but you need to be mindful of not feeding in material covered in dirt, nails, etc.
I made the mistake of trying to sharpen the blades on my grinder - bad idea. Unless you have professional sharpening equipment that will preserve the angle etc, send them out. It''s worth the $20 or that it costs.