Td5: rear suspension acting up (and down)

Have a 2001 Td5 with 206 K on the clock.
Drove to Galway this morning ( approx 20 mls @ -4/5 C ) - no problems until end of journey when I thought I had a flat .
Turned out the rear suspension had gone down on both sides - (yellow light illuminated on dash ) .
Parked it for a while - started up , light off , suspension came up to normal .
After a few miles - light on , down again. Switch off , wait a few minutes , start up and another mile . Light on , suspension down to bump stops etc .
Was about to give up and have it recovered when I noticed light was on BUT suspension did not go down .
Drove home with light on but suspension as normal .
I was considering a change to coils but as it would take a few days to get the kit I would appreciate any advice as to what I coiuld check in the meantime ; do my own repairs mostly but haven't had much dealings with rear suspension apart from changing an air bag last year - the other had been changed when I bought it over 2 yrs ago .

The good thing about the air suspension is it is actually pretty darn simple (not in comparison to coils but hey!)

I actually bought my TD5 with it converted to coils by the previous owner, and put it back to airsprings for insurance and towing reasons (it is a 7-seater).

The compressor is clearly working as it's able to pump up the air springs, so the question is why it's deflating again.

Either:

air springs have a puncture (unlikely if both sides are going down evenly)
Air harness pipework from valves to springs leak (again, would have thought unlikely if both sides are going down evenly)
ride height sensors are giving bogus information prompting the SLABS ECU to deflate the springs.
Valves in compressor valve block are leaking

Worth a go at covering things in soapy water and see if you can spot what is happening. I'd suggest having a look at the ride height linkages - the rubber rings have a habit of splitting as the aluminium inserts swell up as they corrode.

David

Thanks david - the bogus information makes sense as they go down at random ; but going down too often now , sometimes after half a mile or so .
Will have a good look at ride height sensors - have had no problem with the air suspension since I got the Disco so maybe could hold on to the air.

PS They are about 20 something quid each off fleabay and very easy to fit!.

Checked out the height sensors today as far as I could - checked all linkages were free and electrical connectors in good condition .
Put all back - after about a mile or so light came on and suspension went down .
Would one faulty height sensor cause both sides to go down together ?
When I took wiring plug off the nearside one today I could hear air being released .
The off side one had no apparent effect - but maybe there were both gone down at that stage .
I presume these sensors can't be checked off the vehicle ?
I need the Disco in the present weather conditions we have here and I know the main dlr will be expensive for the sensors .
If I can get the kit tomorrow I will change to coils to get going again .