If you mean their guarantee of satisfaction, not nearly as well as they did when they were the biggest retailer on planet Earth. The question is, did they quit honoring that warranty because they're no longer the biggest, or are they no longer the biggest because they quit honoring that warranty?
I don't believe Sears ever warranted power tools for life, just most hand Craftsman tools, but excepted from that lifetime warranty are Craftsman measuring tools (calipers, torque wrenches) and cutting tools (saw blades, drill bits, router bits).
Could it be the motor brushes?
If the Sears part number is still legible, try Sears.com since they have service information for quite a few of their products and other brands.