We know syntheic fluids used in industrial gear oil conclude PAG and PAO (and/or ester). When we test the performance of these two types gear oils, the properties of PAG gear oil is poorer than PAO gear, such as rust prevention (B method for syntheic sea water), demusibility (ASTM D2711). Is PAG gear oil not suitable for used in condition which water exists? And How did we test the demusibility of PAG industrial gear oil? Does the rust prevention of PAG industial gear oil only reach A method for distilled water in ASTM D2711?

Chemically PAG as a glycol is an alcohol and it is hydrophilic (combines easily with water). In that regard, it will never demulsify like PAOs (hydrophobic).

Use PAGs only in applications where temperature conditions exceed the area of PAOs, that is 130 to 180 degrees C (240F to 400F)
PAG leave less residues when they evaporate at high temperature. or...don't use PAGs at all. If the problem is heat and water, apply good ester based gear oils that are resistant to heat and demulsify very good. difficult to find though. Use proper seals for Esters, consult your seals or lubricant supplier. let me know if you cannot find them.