Sorry about the problems you've been having.
I will add that what drives most owners to sell their aging vehicles is the sheer frustration with the local indie's (or dealer tech's) inability to troubleshoot problems without throwing parts at it.
$6400 worth of parts and service and the original problem still persists?
I would venture a guess that if the right technician got a hold of your car early on and diagnosed the problem correctly, you would have faced far less intimidating costs, and a reliably-running MB as a result.
There have been times when one tech would recommend some expensive replacement of parts when another would say a vacuum hose or clogged injector was at fault. If you followed the advice of the first tech, you would bemoan the expensive maintenance costs of the vehicle. If you had the latter as your technician, you would praise the ease of serviceability and low maintenance cost of the same vehicle.
I guess you had the first tech doing the work.
Good luck with your new purchase...
