40 ppm at 65 °C is not critical for moisture, because at this temperature the oil saturation level is high and relative saturation is likely low. The more serious concern is tan delta > 1, which usually indicates oxidized or contaminated oil, high acidity, or conductive aging products. DP = 520 means the paper is aged but still serviceable, so slowing further aging is important. An online dryer can help stabilize moisture and protect the paper, but it will not correct a high tan delta. First, check TAN, IFT, resistivity, and DGA. If oil quality is poor, oil reclamation or replacement is needed before relying on online drying.