A method of manufacturing a vehicular slider window assembly includes providing at least one fixed window panel, attaching upper and lower rails at the fixed window panel, and movably disposing a movable window panel at the upper and lower rails. Elongated sealing portions are formed by forming base portions of the respective elongated sealing portions via a first shot injection molding process using a polypropylene material, and by forming elongated sealing lips along the respective base portions via a second shot injection molding process using a thermoplastic elastomer. The elongated sealing portions are joined at adjacent ends to form a perimeter seal. The perimeter seal is adhesively attached at a surface of fixed window panel so as to circumscribe the opening and to seal against a surface of the movable window panel when the movable window panel is in the closed position.