The vehicle will need checking on a diagnostic tool to see what codes are present in the suspension system but the most common problem is a faulty air suspension compressor either not working at all or not building any pressure when it does run.
If it is the compressor then I would check for any goodwill from Mercedes - here in the UK we usually get some or all of the claim paid for by the factory on these. Your dealer would need to check this for you.
Cost wise if you did need to pay the compressor works out around $400 or so from memory and around 1.5 - 2 hours labour to check & replace.
Best regards, Paul