I recently bought an Adam expansion module, and of course the data drive wasn't working. I took it apart for repair and found that the sensor was torn to shreds.
I haven't seen any for sale, so I thought I'd try my hand at making one. In my first attempt I made a round disc from thin plastic, used a razor to scratch the surface in a pattern similar to the original and glued it to the aluminum shaft. This was a total failure.
In attempt 2 I made another disc, but used a sharpie to draw thin lines like the original sensor had. This one didn't function properly, BUT when I manually spun the sensor it did cause the drive to respond. It made the drive motors spin in opposite directions though, effectively locking up the drive.
I'm thinking of attempting a 3rd sensor using tiny pieces of wire glued to the disc in case the sensor uses induction rather than optics, or maybe both....but the moral of the story is that I believe its possible to create new sensors for all those dead data drives setting around!!!