In most cases, FuooTech's Oil Filtration plants will resolve the matter and ensuring you have correctly fitted desiccant breather will help maintain the transformer oil is a suitable condition. Also see "How did moisture come to be in my oil?".
Please note desiccant breathers do need to be replaced from time to time, depending on the how the transformer used and sited.
Moisture should be kept below 20 PPM. Moisture, along with heat, leads to oxidation and "sludging" of the oil.