On my recently acquired '84 245, the automatic overdrive is not working. After reading many posts and doing much research on the car, I've determined that the button on the shifter is functional and getting power, the relay is functional (repaired) and getting power and that the white wire from the relay to the 'cup' in the tranny tunnel is getting power when the button is activated. The solenoid has been replaced with a confirmed functional solenoid. I still don't have an overdrive. The only two remaining possibilities (in my guesstimation) are the short wire from the connector just under the carpet to the through-the-transmission-tunnel connection to the solenoid, or the tranny itself. Obviously, I'll be checking out the little piece of wire before rebuilding the tranny, but here's my question(s).

Statistically, how often do the trannys/overdrives actually go out? It shows 160K+ on the odometer, but I suspect a replacement speedo/odo, making the actual mileage anyone's guess. And is it more recommended to rebuild a tranny or replace it with a low-mileage salvage (if available)? And are there interchangeable trannys in other models?

Thanks, again, to all the excellent providers of wisdom hereon.