Abstract: An oil filter is disclosed as having a filter enclosure provided with oil inlet and outlet ports adapted for communication with the oil circulating system of an associated oil lubricated engine. Disposed within the enclosure is a filter element fabricated of any suitable filtering media. In addition to the filter element, a body of an oil soluble, relatively solid polymer having oil additives compounded therein is disposed within the enclosure. The polymer body is located within the enclosure so as to be in an area where minimum oil flow occurs, i.e. in a relatively non-turbulent oil flow area, which results in the polymer dissolving at a relatively uniform or linear rate so as to prevent undesirable concentrations of the additives during the effective service life of the filter.