May be a sensor on the way out or a short in the wiring from the sensor to the transmission control unit.
Although it is an externally mounted sensor, getting to it can be a bitch and may involve a fair amount of labor.
Hopefully you will not have to deal with it.
In my experience with failed speed sensor, it will do it once on a blue moon, then more often then finally the code will never go away.
I know what you mean with longevity, but sensors can and do go out every now and then. Happens across the board with any and all cars.