Here's where I documented servicing the valve blocks, I believe others have used the O-rings that I used and have had success:
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...
