Its literally 10 mins on top of a lowers service.
Just remove the circlip .. pull out old airshaft and push in the new one.
Most important thing is decent circlip pliers (decent but £££) .. got mine at Halfords for about £10 or less ??
Pull off lowers using 5mm hex wrench to release bolts after removing reboud know (2.5mm hex I think) (or better a use long straight extension with 5mm bit as its easier to hit with a mallet than a allen key) = give a good clean with isopropyl and inspect seals…
Now remove airshaft … Push down on plastic lock part that stops circlip rotating.. rotate a bit and get the pliers in and pull out (noting sharp side of circlip and might need a good yank so put end screw back in ).. Assume its a Deb spring, they are much easier than the old as the plastic retainer is better designed.
Reassemble stick in new 35mm foam rings and add oil as in service guide amounts … (I use the Fox Gold in the lowers) .. stick in new compression washers and a retainer and do bolts back up… all done
You need anything in a rush you’re welcome to borrow pliers and scrounge some oil/foam rings/compression washers