First post on this page shows some videos on servicing the front valve block (rear is the same but it's much harder to remove the valve block!), there's also a link to where I bought the replacement o'rings, I also used some silicon grease when installing them, the car stays at normal height for weeks on end:
www.landroverworld.org
2012 LR4 Reluctant to lower from off-road suspension mode
Changing the dryer, if you have a Hitachi compressor, is straight forward. Hardest part will be disconnecting the hoses from the back side of the compressor (intake and exhaust hoses), and re-installing the compressor bracket when you reassemble due to a hard to reach bolt that need to be...
