ok here it is when at rest the rear of my disco td5 sags. normaly the passenger side but does happen on both, at first i thought it was the air bags, but on inspection i have found that they are good as new. no wear on them at all.

so i am wondering if anyone knows what else could cause this problem

cheers

It's almost certainly a leak somewhere. Pump up to full height and get some soapy water. Check out the bags, connections, valve block etc.