Most extractor fans have an oil cup located near the motor. Over time, this cup can become full of oil, causing it to drip onto the fan blades and housing. If your extractor fan is dripping oil, you should first check the oil cup to see if it needs to be emptied. If the oil cup is empty, then the problem may lie with the fan itself. It's possible that a seal has failed or that there is an issue with the bearings. In either case, you'll need to contact a qualified repair person to fix the problem.