UPDATE:

The issue I determined was not a bad leak down pump but a melted plastic on fuel pump around one of the connectors. This melted plastic allowed fuel vapors to leak into cabin and out of the car.

I was able to fix this issue.
My fix included:
- replacing the gas cap (I don't think it was the problem)
- replacing the seal, clamp, top retaining "C" clamp on the fuel tank pump under the passenger rear seat (I don't think this was a problem)
- pulling fuel pump up and after disconnecting the connector noticing one of the pins had melted plastic around it. I filled the hole with JB Weld and connected the electrical connector to hold the assembly together until jb weld dried. Obviouse repair would be to replace the fuel pump. (this was the apparent problem)

Al in all I understand that the original firmware in the x5 sends too much current to the fuel pump and it keeps connector hot, melting plastic around it. I had new firmware loaded a year after I got the x5 (car was five years old at that time), but the damage was already done.

I did the repair about two months ago, all is good now.