Can MS tell if I opened my 360?

So about a week before they extended the warranty, I opened my 360 to clean it since my room is kinda dusty. Anyways, I did it rideculously careful and there are no marks what so ever. But will MS still be able to tell that I opened it? This is an original launch unit, and it finally crappe dout on my about 20 min ago :-(

If MS will be able to tell, then should I just get a new one? And how long should I wait? When will we be able to know for sure about the 65nm chips, and are ones with HDMI on the store shelves right now for $350??

Because the warranty had been over for like over a year, and i wanted to keep it clean, ya know, like how your suposed to keep a computer clean.. how was i suposed to know they would all of the sudden implement a three year retro active warrenty!

Now then, do we know if the new premiums, the ones with HDMI, do they have the 65nm chip? How will we be able to find that out, and what is the advantage of that new chip?