I have an 06 R350 without Airmatic that has a squatting left rear that sinks to bottom at night and never quite makes it up to normal level during driving. Compressor is new, no leaks at lines or air bellow. I am thinking it needs a replacement valve block, but I have searched many online parts stores with no luck. Anyone have a suggestion as to where to find one, without going to MB dealer? Any tips/suggestions on replacing it?