[...] PROBLEM: The cursor always slowly moves to the lower left. One pixel every few seconds1.[...]
I had the exact same issue2: painfully slowly drifting Trackpoint on my X250, never stopping. I'm aware of the Trackpoint self-calibration, I had that on the X200, on the T400, and on the T500, but this was different. If you have the pointer moving fast or just rarely on it's own, that is normal. In my case, it never stopped.
The really surprising thing was that this only happened under Debian Stretch (RC2) and not under Ubuntu 16.04, so I started looking around
Note: it's probably serio2, but could be 3, 4, etc., depending on module load order and number of input devices.
# ls /sys/devices/platform/i8042/serio1/serio3 bind_mode driver id mindrag protocol resolution speed upthresh description drvctl inertia modalias rate resync_time subsystem ztime draghys ext_dev input power reach sensitivity thresh drift_time firmware_id jenks press_to_select resetafter skipback uevent
Most of these are pretty much undocumented and so far none of the GUI configuration managers supported them. The 3 interesting ones are
speed in this case.
Despite this fix, this is most probably a hardware problem, so consider replacing the keyboard, especially if it's still under warranty, though if it doesn't happen under Windows, this will be near impossible to get through the service.
Most will recommend to lower the sensitivity, but that doesn't always work or help.
echo 2 > /sys/devices/platform/i8042/serio1/serio2/drift_time echo 180 > /sys/devices/platform/i8042/serio1/serio2/sensitivity echo 50 > /sys/devices/platform/i8042/serio1/serio2/speed
Keep it after reboot
systemd-tmpfiles --prefix=/sys --create sensible-editor /etc/tmpfiles.d/trackpoint.conf
w /sys/devices/platform/i8042/serio1/serio2/speed - - - - 50 w /sys/devices/platform/i8042/serio1/serio2/sensitivity - - - - 180 w /sys/devices/platform/i8042/serio1/serio2/drift_time - - - - 2