oil leak from air inlet filter

Hello Achmad, When does this happen? When the compressor stops, or when the compressor changes from 'load' to 'unload'? If it happens when the air compressor stops, then please check the inlet valve - does it close completely? Also check the check valve and oil stop valve which are normally found below the screw element. If it happens when the compressor switches from load to unload, then please check the oil level. is it too high (over-filled?). Also, this can happen when the compressor cycles between load and unload very often / quickly. Hope this helps and would love to know when you solved the problem. Thanks, Cas