If you can't correct it you can add a desiccant dryer to the line .

Such as : https://www.harborfreight.com/air-tools-compressors/air-compressor-accessories/inline-desiccant-dryerfilter-64637.html

Harbor Freight used to sell desiccant filters constructed like the one incorporated in the regulator but I don't see them now .

But any desiccant filter installed prior to the supply line will work .

There may be just enough water vapor making past that filter bowl and then condensing out in the supply line to the airbrush .