Yes all seals are replaced in the damper as part of the Full service which is a strip, clean, optimization of all parts along with replacement of all seals gas and oil along with Polymer Du eyelet bushes.
Farmers Choice is a little optimistic on the ‘others’ prices 😉
You cn get squelching from the shock in the first bit of the travel as the float fluid in the air can is transfered between the positive and negative air chambers in the air can.
It can also be nitrogen in the oil, if the shock has not been service in the last 12 to 18 months it’s more likely to be cavitation. In the worse cases of this the damping will become more effected the hotter the shock gets through use giving inconsistent damping.