The 17.5 AER Fork received an update to the Air piston. We have found these to feel better with less friction after they are torn down and greased. The OEM grease is not sufficient and is grabby in the beginning of the range. We are updating all the older forks with this piston and the better grease. This is a great fork and a good design but needs some attention. Send us your fork and we can get you updated with the new piston and re-valve at the same time.
Read more here about the works mid-valve.