A quick way to find a leak in the air suspension is to get your hands on an old A/C sniffer, which you can easily find on Ebay, and toss in a car of R-134 through the air tank under the front fender.

You might have to build your own hose to make this connection, but after you charge the system with a can of R-134 you can use the sniffer to detect even the tiniest leak.

Mercedes told their techs to never do this, but a lot of them did anyway. I learned this trick from an old tech that used it a lot back in the 70's.