Check lab records to determine the need for repair. The most likely cause of problems is a leaking O ring or internal seal, or a loose plunger. Regular cleaning is mandatory after each use. Routine maintenance is required at least monthly.
Unscrew the body of the pipette according to the manufacturer's instructions and remove all parts. Inspect and replace the nozzle insert if required. Clean the inner seals and clean and lubricate the plunger mechanism. Replace inner seals if needed. Any other repairs will need professional servicing.
Replace all parts and clean off the outside of the pipette. A simple calibration check can be made by using the MLA calibration kit and comparing the results of the pipette against those obtained with a newly calibrated and certified pipette. If this result is not satisfactory, the pipette will need scientific calibration against known standards using gravimetric analysis.
Send the pipette to the manufacturer for scientific verification, calibration and repair if your laboratory is not suitably equipped. In-house calibration of the pipette can be performed if the laboratory is properly equipped with a gravimetric balance, a hygrometer, MLA calibration kit and a controlled environment.