So I've been reading through many many of the odometer problem posts, and I could only find one that described similar symptoms to my problem:

http://www.brickboard.com/RWD/volvo/1415770/220/240/260/280/odometer_works_sporadically.html

The symptoms are the speedometer always works flawlessly. The odometer/trip meter, however, works about 60-70% of the time. It will randomly cut out and not roll at all. Often, though not always, a sharp "whack" with the palm of my hand to the top of the dash will get it rolling again, and it will usually continue to work for quite a while. It's hard to notice, but I believe it usually stops working after hitting a bump or rough patch in the road.

To fix this intermittent failure, my questions are:

1) Could it still be a broken gear that somehow catches with the "whack"? Or, does the odometer fail permanently once there is/are broken tooth/teeth?

2) Does this sound more like an electronic failure? Did the 1992 240 speedo units suffer from the same capacitor failures that are talked about in the 700/900 FAQ's? If so, what should I be looking for and where?

3) Could this simply be a weak soldering point or points? Given that bumps and whacks are what affects the unit?

4) Has anyone else had this intermittent failure problem, and have suggestions on how to repair, or shared experiences?

Thanks all in advance for your assistance.