How to save 275kV Transformer with Furan content exceeding 4500ppb

Hi All,

Something to share and i request your advice and opinion on this issue ?

Currently i have 275kV transformer with Furan exceeding 4500ppb and moisture in paper > 4.0% ( FDS measurement), and this situation originated due to ageing oil insulation This is thermally non-upragraded paper insulation designed at 55 deg C, i have some concern if the transformer is safe to be in operation? any recommendation to safe the transformer and do FURAN is a good indicator to make judgement to remove the transformer from service. All the electrical test within limits including pf at 10kV..

Really need your assistance. Thank you