Leakages on seals despite very good oil purity?

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?



OELCHECKER Summer 2013, page 8