How do I know which of the Air-Springs L or R, or if their seals are leaking air on 2003 Mercedes-Benz E500

Rear-end of car on both sides goes(Sags) down after (30min) car turned off, goes up when car starts up (w/in 5min). How can I know if 1 or both Air-Springs or any of their seals are leaking air? Could 1 seal be leaking & not both or an air-line damaged & not able to maintain the air pressure? Problem is constant. Thanks

Asked by for the 2003 Mercedes-Benz E500
only can be properly diagnosed at dealer or independent shop with star diagnosis machine. be aware
that if rear bags are bad it is a very expensive repair due to extreme amount of work involved.
thanks Jim, I need to ask you @ dealer each of "air-springs" is $847, web "belestiens it's $620, should I buy from web the L & R & have a mechanic change for me, it will be cheaper than the dealership, as for them to diagns. it's $112. NOTE NOW IM NOTICING ONLY THE REAR LEFT IS SAGGING & NOT (ANYMORE) THE REAR LEFT? SOMEONE TOLD ME IT COULD BE THE SEAL ON 1 OF THEM GONE BAD? DO YOU THINK OF I CHANGE THE REAR RIGHT SIDE AIRSPRING WOULD MAYBE SOLVE THE PROBLEM?? I WOULD APPRECIATE YOUR RESPONSE!!