A method for dispersing an oil additive into an oil passing through a filter, the method comprising: filling a first cavity of an additive cartridge with an additive; locating the additive cartridge within a housing of the filter, the additive cartridge being located within a flow path through the filter, the additive cartridge having a second cavity without any additive disposed therein, the second cavity defining a first fluid path through the additive cartridge and the oil must pass through the second cavity in order to exit the filter; and metering the additive through an opening in the additive cartridge, the opening providing a second fluid path into the additive cartridge.