That's because there is no paperwork. They know based off the VIN number when the car was purchased and how long the warranty is. On your 04, the bumper-to-bumper is 3yr/36k miles I think, so if it was originally purchased before June 13, 2004, then the full warranty has expired. If it was purchased later, then you have the full warranty until 36k miles or until y ou hit the 36-month mark. However, you still have the longer limited powertrain, which is 5yr/60k miles or something like that. You can find out for sure by calling your local Mitsu and asking. For the life of the warranties, you only bring in the car and have them do the work. There is no paperwork that you have to bring - they just know based off the VIN like I mentioned above. The only worry is if you have mods, they may deny warranty coverage.