Any age limitations on that warranty (ie is 2011, never serviced pushing it)?
2 years from purchase, isn’t it?
OK so I am planning on getting the Epic Bleed Kit and this seal kit is that the right kit for a rebuild?
I think that seal kit will just about get you there, but it doesn’t include a new main piston seal (which *I* think is related to the sagging problem) – seems a shame to go to the trouble of dismantling it and not do the full monty, but YMMV. You may be able to get a local bearing factor to match the piston seal (I would put the original back rather than use “one that looks right” from Screwfix, etc.). IIRC the piston and IFP seals are in the full service kit (circa £50?). There is conflicting information on the internet about what size these O-rings are (some say metric, some say imperial. Both cannot be right).
There are specific SRAM tools for setting the IFP height and bleeding / setting the oil level which you may decide you need, but I don’t believe they are essential once you have figured out what they are designed to achieve (the IFP height is not terribly critical, IMHO). I found this very useful.
Be very careful as you undo the inner seal head – the air that is causing the sagging is bottled up behind the main piston and/or the IFP, both of which are held in by the inner seal head and could still be at 100PSI+ (there’s no way of safely bleeding the air out AFAIK).