Hi bought a second hand compressor when i picked it up there wasnt any oil in the compressor i think its leaking down from the inspection glass as i could see a little run of oil under the glass and also when i drained the tank of air underneath there was a bit of water and i think bit of oil mixed in it, its not black stuff just clear. It ran good and sounded ok. So my question is is it normal to have oil and bit of water in the tank and also is the oil inspection glass easy to replace? I bought it as it was cheap £80 fir 150l tank and 3 hp pump.