My GL450, one side is down and the other side is up. I was told the right rear air spring(bag) is blown which it is. Before, my gl450 sits low when off but when on, it rises up. However, after getting new tires and doing an alignment, one side would not go up. My problem happened right after new tires and alignment was done. Took it to mercedes and they told me that the air bag is popped, but they also want me to replace all FOUR level sensors and the left rear air spring(bag) too. They want level sensors replaced because they are bent/ corroded plus the right front air strut due to it leaking. Do I have to replace sensors or can I just replace 1 or 2 of the air bags? I didn't mind my car dropping when off but cant I just replace the popped air bag?? Please any advice would help. The repair bill they gave is 4000 dollars.