For your safety I recommend that you have someone who is familiar with hp compressors, filter systems, oils, hp fittings, etc., have a look at your rig if at all possible. It doesn't sound like you have an actual purification filter chamber after your final moisture separator, but with no photos I can't be sure what you have.
I made some mistakes in my early years of dealing with hp air systems that could have been dangerous while I was still learning things the hard way. I still see people using low pressure pipe fittings that come from the local hardware store, and lots of other potentially unsafe things, particularly at small volunteer fire departments that haven't had the benefit of knowledgeable people building or servicing their equipment.
The older I get the better I was.