So I've been getting the old ping ping suspension inactive messages occasionally although becoming more frequent, plus I can now here the compressor working especially on start-up. My ID tool shows fault codes C1131-92 (6C) "Air supply - component failure - performance or incorrect operation" and C1A20-64 (6 "Pressure increase too slow when filling reservoir - Algorithm based failure - signal plausibility failure".

At the same time, the car 'sits down' over the course of the week (I'm away Monday to Friday and the car remains on the drive) but comes smartly back up to height once started.

I'm guessing the compressor is on its way out, but is the dropping a signal of something else as well?

Well I've ordered a replacement compressor from Dan at Duckworth's and I'll fit it this weekend. If that doesn't cure things then it will be a new reservoir next.

been much cheaper to refurb the comp pal , especially if it doesn't cure the issue

That was my original plan until I discovered I have the later Hitachi compressor. I was aware of the issue when I bought the car so knew I had some potentially expensive purchases upcoming and reflected these in the price I paid for the car.

So after a false start last weekend due to the wrong replacement compressor, the right one arrived this week and this morning I set to replacing it.

Fairly simple procedure if you've watched the online videos, took about an hour but only because I bled the reservoir pressure through the compressor connection not realising I could do this from my IID tool

Once everything was reconnected the reservoir pressure came back up to 1540 and I went through the full range of heights without the dreaded bing bing noise. Took the car out for a run whilst monitoring gallery pressure and compressor temperature and all looked good, until two minutes from home I rounded a roundabout and the gallery pressure reading dropped to 330. Parking the car on my drive I selected off-road height and the car leapt up and the gallery pressure immediately read 1160 so I'm guessing maybe a defective pressure sensor on the gallery, or am I not supposed to monitor live values when driving?