Most likely the endplay of the rotary magnet is too much and it hit the aluminium casing to which the needle is attached. The bowden-cable may have dried up oil/grease in it hence the wobbling of the needle. Have a look at the meter and see if repairable, sometimes you can fit one or two this shim washeres to reduce the endplay, otherwise the wrecking yard option needs to be explored.
It's all about the dollar! The odometer is direct gear driven from the cable. The speedle needle is attached to a bell which inside two magnets rotate, causing drag against said bell. Your odo shouldn't roll over any faster now that your bell bushing has worn out, allowing it to lock directly to the magnets. That had to be a hoot when she let go! Well, it WOULD have been from the passenger seat, anyway!
Not sure if any of the local wrecking yards will even have a w100 in them. Most around here crush anything more than around 10 years old. We lost access to the older stuff when Missoula auto salvage closed. Phone gps or Canadian may be your only options.
If you go with the NOS Canadian one, design and print a sticky label to cover over the confusing ones that don't match the roadside speed limit signs! Although in the UK most things have to be metric, fortunately road speeds are still in mph. I still laugh at the memory of our then national rail operator announcing the the next generation of high speed train after the 125mph Intercity 125 would be the Intercity 225. After an initial "Wow!", came the realisation they meant 225 kph or 140mph. Andrew.
