There are other threads on this, but I'm starting a new one because I have a solution (this is a duplicate of one on the X300 forum). I'm of the understanding that the one of the most common reason for failure of the seat memory function on X300 and X308 cars is not electrical, but mechanical. The seat position is derived from a potentiometer on the shaft that drives the seat movement mechanisms, one for each motion axis. There are 5 in these cars for each front seat. The failure is not the potentiometer, it is the nylon slip coupling driven by a gear set that reduces the multiple rotations of the shaft to a single rotation within the range of a 300 degree or so potentiometer. The coupling embraces a ball drive element on the gear with a spring clip to create a friction drive that can slip at the end of the potentiometer rotation (that way travel to one seat limit will initialize the potentiometer to the seat motion). The coupling has 4 petals, if one of these breaks off the ball is no longer embraced and the potentiometer ceases to turn. It's a little problematic to get to the 5 potentiometer assemblies, some easier than others, but once there pretty easy to open the housing and withdraw the broken parts. on some of the locations the housing can be opened without removing it from the shaft. There is more on this with pictures on the thread in the X308 Forum. But what to do then?
It took a while and quite a few trials to work it out, but I finally came up with a CAD model that could be 3D printed in ABS plastic as a reliable replacement. A direct geometric replacement did not work because of the peculiarities of FDM printing. So here it is:


This is shown on the gear. I also found that a installation alignment tool is also necessary to easily snap the coupling on the ball. I've cycled this final iteration on and off the ball many times without breaking the coupling; I think it's good to go. I'll get the coupling and tool on eBay later this week for those who are interested. Glad to have finally finished this project.

 

Looks like some nice work...cheers to your motivation and success.