My 2006 SL500 has developed a left rear sag after I park it for a few days... I called the dealer and of course he tells me all the worse news I could ever want to hear. Is this the valve block issue I have read about or the shock on left rear side. I have seen no fluid on the garage floor anywhere

 

You have a 14 year old car. Time to take it to the dealer.

 

That's pretty good performance, and there is nothing abnormal about your rear valve block. An internal clean of the valve block may get you a few extra days, but I personally wouldn't bother. The clean could be done by executing two 15-minute "Rodeo" routines back-to-back. I know of just two diagnostic systems that can perform a Rodeo: A $200 Star Diagnosi; a $130 Foxwell NT510.

 

Exactly what I had about a year ago. Cured by a valveblock rebuild using one of the rebuild kits from eBay.

My memory is hazy and I’m in UK but price of a kit was approx £55 Sterling/per kit and my mechanic charged £300 Sterling labour for the job as I chose to have both rebuilt at the same time.

Once off the car there was clear evidence of degradation in the seals, so for me it was definitely the right move.