The PM-SM does controls the seat & steering wheel movement...as well as the
123 M memory function on the e53. But the GM could also be the culprit since it is the major control module for items on the P-bus.
The issue with the steering wheel column...could also be the connection to the drive for the motor that tilts up/down. To check this would require removing the panels below the steering column. I don't know if there's a DIY on any e53 forum for this problem...but there should be something in the e38/e39 DIY forums/sites for this issue. I've seen it discussed and written up before. The DIY for an e46/e38/e39 would be 99% similar to that for the e53.
