An inkjet printer and method therefore including a detector to monitor a quantity of release agent applied to a spreader drum. The inkjet printer includes a drum maintenance unit which applies the release agent to the spreader drum with a metering device, such as a metering blade, and determines a flow rate of unused or excess release agent returned to a release agent sump. The determined flow rate of release agent provides a determination of the quantity of release agent applied to the spreader drum. Upon the determination that too little release agent has been applied, at least one function of the inkjet printer is disabled to stop the flow of release agent and to facilitate maintenance if necessary.