This sleeve takes care on Type 2 11/63-07/67 and  Karmann Ghia 66-07/67  of the connection between air cleaner and carburettor, so that only filtered air can get into the combustion components. Temperature fluctuation and corrosion by oil and petrol vapors can render the sleeve fragile and porous. It gets damaged and there is no longer a good sealing. From now on you can replace your damaged item.