The two motors in my GBC got tired of overcoming its high friction and starting jamming and making ominous clicking noises. I decided to sacrifice one by using it as a publicly-accessible hand crank for a public display. I assembled the crank, starting cranking, and the motor jammed. I did what any spectator would do, and kept cranking. The sacrifice was complete--the shaft turned freely, but it no longer generated any electricity. So, I did what any tinkerer would do. I took it apart to see what broke. Compared to other Lego motors, this one came apart and went back together nicely. Full resolution photos are available here.
Here is the motor (upside-down) with an axle inserted
Using a Phillips precision screwdriver and a lot of initial torque, I loosened the four screws on the bottom then pulled off the bottom cover.
I gently pulled the circuit board out of its slot to give the wires some slack,
then slid the motor and gear assembly out of the top housing.
The gear assembly separates easily from the motor, at least in my case. Looking through the hole where the motor shaft belongs, I immediately see the problem.
The front and back pieces of the assembly separate themselves. You might be able to see in this photo that my center spur gear is in two pieces.
After removal of the top-most gear on the left and the gear on the right, it looks like this:
With the remaining gears removed, you can clearly see the gear split into two pieces. No other gears have obvious damage. After fitting the broken pieces back on to the motor shaft, I at first thought I might have missed a third piece, because there was a gap between the pieces. Then I realized the gear's inner diameter must be smaller than the motor shaft diameter, and the two pieces were forced together to provide the friction needed to lock the gear in place. This is probably the weakness in the design, because it means this gear is already in tension before any load is put on it. Given how easily the motor disassembles, I wonder if some enterprising AFOL might find a way to remediate this flaw.
Heres a picture of the entire disassembly. Well, the broken gear does seem to be missing in this picture. (I think the backdrop is the silent cry of the motor wishing to be whole again 
.)
Finally, some fuzzy close-ups of the little circuit board in case you wanted to add up the stripes on the two resistors. I had to bend the capacitor out of the way to make them visible. You can read the capacitor better in a previous photo.
That's it. I'm trying to decide what to do with this now. It went back together as easily as it came apart. I briefly thought about gluing the broken gear, but knew that wouldn't hold and I wouldn't be able to get the gear tooth spacing right at the break points anyway. The housing would make a sweet box for custom electronics if I were into that, but I'm not. I guess I'll just put it back in the bin until inspiration comes. Meanwhile, I'll just end with the lesson learned: don't use the 47154 motor heavily loaded.
Have a nice day!