Rear right body is lower / dropped

Except while washing the car, I noticed that the rear right body is lower than the other three. I have ensured that all four tires have the same pressure. I also do not get any warning/error message from the dash. The maintenance option in the dash says "No Malfunction". While driving it, I also did not notice that the car make any strange noise or the tire rubbing the shock or any other part of the car.

Has anyone experienced or seen similar issue?

I hope it is not the strut that goes bad. S430 uses an automatic shock and a new one is approx. USD$1100. Is cause may be: (1) Leveling gauge goes bad (2) Leveling gauge needs reset (3) Leak. How much approx. to repair it labor & part?

Any advice is greatly appreciated.