<p>An annular elastic portion is secured to an annular metal core portion. A through hole is provided which penetrates the metal core portion and the elastic portion in a radial direction. A porous member which has the properties of allowing free passage of air while inhibiting the passage of water and oil therethrough is secured to an outer peripheral surface of the metal core portion so as to completely block a radially outer opening of the through hole. An canopy member having a cover plate located on a radially outer side of the porous member is secured to the outer peripheral surface of the metal core portion.</p>
