R350 strange suspension issue

Hi all, i have a 2007 R350 4Matic.

I have a strange issue going on so please excuse the length of this post.

When I drive the car for say an hour or so I get the riser malfunction i.e. the car icon with up
arrow and malfunction text. This weekend I drove to Vegas and not only did the former
happen but also the "STOP, car too low came on". Stopped for a while, the car rose again
and same repeated. When I parked the car overnight same issue the back wheels were
completely depressed. On the way back same issue over and over. Had to stop 3-4 times for
it to rise. I did notice the left rear was more depressed than right rear. Please note all
throughout the outside air temperature was like 105-112F.

Now, when i came home, started the car this morning, it did not even complain the car is too
low even after a full night stop.

Is it possible that the left rear air-bag is malfunctioning after 1hr of driving or after driving in
extreme conditions? If the pump was faulty the car would never rise correct?

Any ideas here would be very, very helpful.

Also, is it OK to change only one airbag or recommend both?