Power seat problem

[420SEL]

The driver's seat in my '99 E430 recently developed a small problem. The seat will not move backwards when you press back on the control. It moves forward instead. All of the other functions (up/down - recline/unrecline - tilt up/down and headrest up/down) work fine. Even the seat forward control works fine. It hasn't been a real problem, since when I use the pre-set memory the seat will move backwards to its set position. I plan to get it looked at next time I take the car in, but I was hoping someone might have some insight into the cause of the problem and size of the solution.

Thanks.