Hey John, sorry it took me so long to find time to look at this thread.

First of all, you're a great guy doing the right thing. This is exactly what I'm working at and will do when I sell. A nice clean perfect as possible car and assistance so that they don't break the bank everytime they need something diagnosed.

As far as the issue, I'm wondering why the tech said that they couldn't pull any codes... That literally makes no sense because the first thing to pull on DAS if there's no CEL is the "Full list of Fault Codes and Events" on the home screen of the ME. It pulls up every single code that has ever been thrown on the car including stored codes that may clear themselves after the problem goes away.

It's hard to say why it would happen and then go away, but Buckhead at this point knows the car. I put my money on them being able to come up with something. Tuning is crazy from what I'm trying to learn on MB's and there is always a possibility that they changed the wrong value on coding somewhere. Happens all the time.