We have detailed with pictures in our book how to repair the most typical card reader repair: the "gummy wheel" problem. This appears when the original material that was used to move the card disintegrates into a gooey mess. This is covered both in the book but also on a number of other websites.
We have found also another type of damage: a similar disintegration in the material between the engine axis and the endless screw that transfers rotation to the wheel. It shows in the noise of the transprt (which is the endless screw skipping over the engine axis). This will appear in the next version of our book. It basically consists on:
I will include pictures once I have done another fix.