Fill-nozzle O-ring replacement

As the fill nozzle O-ring (QWLV050004) ages, it looses its flexibility and air-bubbles may occur in the Westergren pipettes, the O-ring needs to be replaced.

Symptoms for a bad fill-nozzle O-ring
After the aspiration, the Westergren pipette has a zebra pattern (air- blood- air -blood, nicely divided in the column.)
Vacuum stabilisation errors may occur.