First thing you should do before you start to clean you dies is to take a mental note of how they go together so you don’t assemble them wrong after you’re done. Once the dies are disassembled you can us a wire brush to clean the serrated teeth and remove all dirt, paint, and metal deposits. The teeth are what grips the sheet metal surface and pull it together in the case of a shrinking die and apart in a stretching dies. You do not want to be too aggressive in the cleaning of theses teeth. You could possibly round over the edges resulting in poor tool performance.
One trick for old and worn out dies is to the rotate the dies 180 degrees. Make sure to do the top and bottom set of dies. The edge closer to the operator tends to ware faster than the far edge. So all you need to do if flip them and around and you’ll be able notice a difference in the performance of an old set of dies.
Another trick to enhance the performance of your shrinking and stretching tools is to smooth out the mating surfaces of the die sets. The v block that houses the two blocks with apposing teeth have surfaces that contact each other. These surface rub on one each other as the die sets are pressed together and retracted. After taking the time to smooth and lubricate these surfaces will feel and see a difference in the operation of the tool.
I came across this video by Performance Motorsports Internet TV. It has section that show how-to clean and maintain dies. If you want to skip ahead to the section that talks about maintenance of shrinker and stretcher dies fast, forward to 6:22.
