Since the original topic was archived, I had no choice but to leave the message here. After separating the motor from the drive slot assembly, I found out that the rubber coupling material (as described here ) was decayed and could no longer hold tight. I put some droplets of super glue on the motor shaft, placed it back and the gear spinned favorably this time. The card reader now works like a charm again (the screen says working, too! ) even with a pair of slightly smaller sized (6mm) o-rings!
Thanks to whoever gives out helping hands (and guides) and many others in this forum!
P.S. To whom has similar problems: please be aware that the screws that lock the motor on the assembly are prone to getting stripped if a screw driver of wrong size is used.
Edited: 5 Sept 2012, 5:02 a.m.