sagging rear end, and its not the mrs

hello peoples, can some one point me in the right direction with a small problem please. my dads got a 53 plate td5 that goes down at the rear end after only standing for 2 days. i replaced the air springs which stopped it going down within a couple of hours like it used to but it still sinks right to the bump stops after 2 days. is there a common fault that some one can point out please, thanks arron.

It will still have an air leak somewhere. Could be on a connection where the pipe goes to the air spring, on the valve block, in the valve block or a hole in a pipe. Try spraying soapy water over all the connections and pipes . Leaks show up as bubbling. Also don't rule out a faulty new air spring. Good luck.