Normal
There are at least two different mineral oil types. I know there are more. I can only remember two of them. (Paraffin, and naphtha.) I guess it would be wise to see what type the Magura oil is. Naphtha is used in mild conditioning soaps (my knowledge anyway), and some skin softener s. Of the two the paraffin based one is probably best for the clutch cylinder. In a lab I remember naphtha going off more actively than parrifin. I don't know why they aren't using a seal that can live with ATF or standard hydraulic fluid.