Well, I opened it up without much success, and took some pictures of the process:
At first I tried pushing/prying the light grey tabs away from the dark gray "bottom", but those weren't budging
So plan B: wedge it apart:
It was opening, but I was also distorting the plastic in the process - perhaps if I had a hot air station or something, I could have of softened it, but eventually it gave way:
I didn't open it just yet, but rather went to work on the other side - I made my way around from the front/back, as it seemed easier than going at it directly from the side. Anyways, it was much easier than the first side, and I got it open:
Nothing fell out, and I didn't rip any wires out by opening it, so I proceeded to take out the motor:
This is where something finally fell out - there was a little "spacer" disk (visible in the top-left) that was between the end of the axle and the back side of the plastic housing.
After that, the electrical connection assembly slid off easily - not sure what the component is or how to test if it's good, but it seems like it was made such that it's replaceable - no solder was used, just metal "crimps"
This is where I found out that the motor itself is good if I just connect a battery to it directly, so I think I may end up drilling some holes and have a DIY wire coming out the back - all the contacts on the inside seemed good and clean, but unfortunately the bottom seems to be rusted to the point of not making contact anymore.
I think it will snap back together just fine, but it will have scars from the surgery.
For anyone curious, the motor itself is a mabuchi 70586, but any FC-280 motor should fit.