Sorry you had bad experiences with MS's repair service. I had similar issues with Sony's back with my large ps2. I played final Fantasy XI on it, an the system locked up and died and wouldn't read any save data from a HDD or memory card. Sent it in to be replaced (paid to send it in). Got it back, same thing. Called support and was asked to resend it in. I sent it back that night (paid again). Then got it back saying the warranty was null and void since tech forgot to replace seal first time. Ended up speaking to high level customer service there with BBB to get them to fix the system.
hopefully your bad service call gets resolved much easier.