Thank you so much for the replies chaps, it's a big help.
It failed a couple of weeks ago, inconveniently at the same time I managed to snap one of my fingers (unrelated !)
and today was the first time I've been able to get the wheels off and have a proper look !
With the ignition on the compressor will run before shutting off, the mmi greys out.
Does not lift at all.
There is a fault code, 02646
Drive motor "b" current sensor circuit range/performance.
This will clear, and the mmi comes back and the compressor runs again, but then shuts off and mmi greys out as before without lifting.
In either scenario when you turn the ignition off there is a reasonably loud hissing for about 20 seconds in one spot only. Its loudest from the top r/h cornor of the engine bay,
rather than with my head inside the corresponding wheel arch.
Not small bore, but there are two rubber pipes in that area of the engine bay, One of which seems to get very cold, very quickly and condensates very quickly.
Not sure that's related, but my knowledge of these things isn't great so I thought I'd mention it !
My gut was a leveling sensor, it used to randomly grey out while driving and ignition off and on again would solve this.
It's also never sagged on a cornor always evenly.
Any thoughts ?
Thanks