Due to the short oil service life, resulting from relatively high temperatures of over 75°C in the hydraulic tank, we changed the oil, around 6 weeks ago, in a few stationary hydraulic systems from a mineral oil-based hydraulic oil to a synthetic fluid. After the change, your lab reports show a residual content of mineral oil of less than 2%. With a value of 17/14/11, the oil purity was very good. There were no negative results. However, larger leakages have appeared on different seals more recently. What can be the reason for this?