I have a 5hp, 2 stage air compressor that is way overdue for an oil change and I don't have the manual, if there ever was one, to see what was recommended. Looking at a few sites with similar compressors I see they sell Compressor Oils, either synthetic or regular that are SAE 30. I have a milling machine that uses ISO 68, which equates roughly to SAE 20 to 30, that also needs a change. Rather than buy multiple oils I would prefer to buy one 20L pail (5gal) of the ISO 68 hydraulic oil recommended for the milling machine and use it in the compressor too. Anyone do the same or have a reason not to? Thanks.