I find that to figure out where an air system problem is, one has to go at it very slowly and with great patience.

Your primary search procedure is the removal of fuse F26E in the engine compartment fuse box. This is the main power fuse for the system computers and kills all the confusing after dark at night rambles of the system. The system is like an alley cat - you do not know what is going on when it is parked.

In theory all the block valves fail closed when the power is removed. In theory this means air pressure is trapped where it is trapped and does not vent into another system.

In theory then, the air in say a front left air spring can only exit either thru a) the rubber of the air shock, or b), the section of air line between the top of the air shock and the inlet to the block valve or c) within the block valve itself.

If you had an block valve problem, and if the cross link valve in the valve block leaks, then air can travel left right from either the front air springs or the rear air springs but not back to front. For the front end to equally drop, that infers a leak in one of the air springs, lines, or thru one of the left or right valves and the cross link valve into the main system which generally is not a pressurized. The reason the main system is not pressurized is so the air compressor upon startup starts "no load." That is why you usually hear the "fart" at the end of a compression cycle - same as on the semis, the air compressor unloading.

The link below is to an air system drawing even if it does not look like it.

DISCO3.CO.UK Photo Gallery - FASKIT Air Suspension Installation/6mm PA12 grade nylon tubing with heat shrink applied

So in summary, spend some time trying to figure out just what your system is doing and then let us know what you did and how the system reacted to each procedure.

Also do you have the NAV with the air system display page? That is also a test device you can you to figure out what is wrong.

 

Guys, Sorry I haven't gotten back on here. Still having issues. Replaced so far:
Both Front Springs, Front Valve Block, Compressor, R Rear Spring. It is still lowering R Rear overnight. Going to take the fuse out and see. My Independent Rover Mechanic can not find any more leaks and no codes are being thrown. Suspension comes right up on startup, it's just f'n annoying.

 

They isolated it to rear valve block. It was replaced and it hasn't gone down since

 

It might be a useful time to remind folks, if your valves are going like that, the dessicant canister probably needs to be replaced and the lines blown out. It makes its way down the pipes and messes things up.

I've got an intermittent issue, well, it's not intermittent it just doesn't fault very often. The fault is too many transitions. Unfortunately it is not actually bad enough yet to find where the problem is, so I think I need to live with it. Along with the rear door lock, which I just don't want to dive into.