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:
pulling the endless screw away from the engine.
Clean with a needle the inner part of the endless screw. There is the material that has dried up and is now skipping.
Fill completely the cavity with E6000 glue. Let dry for a very short while (15 seconds)
Join again the endless screw with the engine axis. Make sure that the glue does not reach the engine body! Remove excess glue.
Make sure the ensemble is straight and let it dry fro 48 hours before installing it again.
Ready! Now it'll sound much better, and it won't skip.
I will include pictures once I have done another fix.