Assuming the ground is perfectly level then one side should not lower. And keep in mind its impossible for one corner to lower and the rest to stay the same. Physics. So if one side of the front is lower than the other than you should check all corners. You could have a leak at the rear brings that side down. But if that is the only corner going down then the opposite rear would go up. So I would really check all corner heights. Also you can sometimes rule out a slow bag leak if you set it to off-road and measure overnight. Cracks usually form at the fold in the bags at regular road height. When the bag is no longer at that height the folds tend to close up sealing the cracks and string air form getting out.

 

The rear isn’t lowering overnight. I can tell that.

 

Then that would mean one rear corner is going up. So then your leak would be in the front only. Bag or valve block is likely. You can try the off-road height test and see what happens. I put money on the block. You can rebuild them all for about $25 and time with rebuild kits. Just a bunch of o-rings for all of the blocks but they are all the right size.

 

‘This is the valve block? https://www.roverparts.com/Parts/RVH...SABEgLK5_D_BwE

 

Yup, thats the one.

 

Raised it to Off-road Height and pulled the battery. Next morning the front end was slumped down to the same height as it did before overnight.

So, valve block is the likely culprit?

 

I would bet as much.