Changed the oil today, and replaced the oil level sensor. I initially intentionally underfilled the oil by 1L (low point on dipstick), and took it out for a test drive. iDrive showed oil level at maximum. So it appears that the oil level sensor may not have been faulty.

I'm going to work to get INPA set up, and run a diagnostic on the sensor. I read somewhere that it is also possible to clear the long term oil level value. I'll report back when I know more.