Cleaning a Lortone TS-8; oil level question

Hydraulic oil is hygroscopic because of additives.  Those same additives make it nasty to your health.  Water intrusion from rain will emulsify when the saw is run.  Milky foam is a good indication of this.  Get it out. It will grow bacteria and get really stinky and hard on your skin.  If it is just dirty, then for sure filter and reuse.  If you read through the archives you will find all kinds of places where people have sourced plain mineral oil.  The most easily obtained is baby oil from Wally World.  1/4" is a good number.