I greatly appreciate the help here. This is where I'm at:

Took the vehicle to my local shop that works on Land Rovers, they said that the reservoir is not releasing air back to the rear suspension due to a stuck or malfunctioning solenoid.

They did not refer to it as the "middle valve block" but I assume this is what they must be referring to.

They said that this could likely be all I need, but that there could potentially still be a leak elsewhere in the rear end but its not showing itself now and they wouldn't be able to know for sure until the reservoir solenoid issue is taken care of.

They quoted 900 and some change to do the job.

Seeing as I have the rebuild kit (o-rings) for all of the valve blocks, and just did the rear one on my own a few days ago, my thought is to pay them the 150 for their help in diagnoses, get back under it myself, pull the center valve block out and clean it, replace o-rings, and see if that resolves the issue.

what do you think?

 

How many hours do you have into this failed attempt at repair? How much money?
If you are mechanically inclined perhaps continuing as you are makes sense…. but I’m all about efficient, proper solutions and outsource to a professional as my valuable time is better spent on other things.

 

There is only one valve in the center block, it is really easy to do. $900 is insane....

 

That's what I thought. $400 for the part, the rest was labor/shop fees. I picked it up, put it on jack stands and pulled the middle valve block out in about 20-30 minutes. I am going to clean it up real good and put the new o-rings on it, reinstall it and see what happens.

It didn't seem that dirty, but its the original one and the truck is 11 years old, so, maybe I will be pleasantly surprised and this will do the trick?

 

I assume when you removed it there was a ton of air coming out of the reservoir? If not, the shop was a little wrong in what they said.

 

Yes, I don't recall exactly which line it was - but one of them took between 10-15 minutes before all the air was out.

 

For any inquiring minds: cleaned and replaced o-rings in my original middle valve block and reinstalled it today. Not a single fault! Pumped up quickly, all 3 heights achievable without any issue or faults. Time will tell as it's supposed to get quite cold again later this week, but for now, I am hopeful. It has remained at normal height all day so far.