When I originally talked to the owner, I asked him if it was ok if I plugged in and checked the car out. He didn't seem to have an issue with that. I asked him to check my name online to make him feel comfortable plugging into the car.
I wanted to look at max REV's, max speed, launch control activations, and adaptations (I can tell what fuel quality he has been using by looking at that). He didn't seem to have a problem with it.
A few minutes ago he called me and said that he didn't want me to plug into the car, and sounded a bit paranoid. I told him that it sort of seemed like he was trying to hide something, and he replied "Then don't buy the car".
So I think given that plus your comments about S54 reliability are making me reconsider.
I think the SMG unit is fairly reliable other than the hydraulic pump which is known to fail. This was replaced on my E60 M5 as a recall. Being that it's a 2003, I think it's past both the rod bearing and oil pump issues that plagued the earlier E46's... He told me that the car had been sitting for a couple years and that concerned me too, as these cars go to hell when you don't regularly drive them.