I have a 2008 GL550. A few weeks ago it started to drop down on all 4s when left parked in normal height mode. When started, it rises back up. Took to the dealer and they say leaking on both front struts and rear air springs. Must replace all. Discovered that when left parked in elevated mode, nothing leaks and car stays up indefinitely. How could I really have leaks on all 4 corners if this is the case? What is bypassed when in elevated mode. No fault codes at all. Compressor was replaced by dealer 1 yr ago. Please help.