Fitted some front Bilstein gas struts to my 8V digi about 5k miles ago. Noticed last night that the driverside one is covered in oil.

Passenger side is bone dry.
I'm immediately thinking the strut is leaking oil BUT they're supposed to be gas struts. Might be a daft question, but do gas struts contain any oil?
I also wondered if it was oil/grease kicked up by something else but the plastic boot in the strut is damp too but the coil spring is bone dry. Would this suggest it is originating from the strut?
Cheers for any help.