Personally I haven't done it, and no worries. But at the first sign of abnormal squeaking, I'll do it.

Yes, I have done that...
see instructions: Finger.34B. When lubricating the treadmill, observe the following instructions for lubricating the treadmill.
1. switch off the device and disconnect the cable.
2. turn the two screws of the support roller anti-clockwise with a hexagon spanner until the treadmill belt has become slack and can be lifted off easily. note: please use the turns of the hexagon spanner to loosen the treadmill belt in order to adjust the tension of the treadmill belt after lubrication.
3. lift the running belt at the edge and spray lubricating oil evenly and in the centre of the running platform.it is not necessary to spray lubricating oil over the entire width of the running platform.4.Lubricating oil quantity for each maintenance: 5 - 10 mL.Caution: if the lubricating oil is overfilled, the treadmill belt will slip.5Use the hexagon spanner to turn the two screws of the support roller clockwise by the previously recorded number of turns until the treadmill belt is properly tensioned.6Switch on the device and perform exercises for a few minutes so that the lubricating oil is evenly distributed over the entire surface of the treadmill.