Overheat issue on Xbox 360Follow

I know this forum is PC-centric, so I won't be too disappointed if I don't get any answers. Worth a shot just in case, looking for some advice!

Issue: Xbox 360 (Pro, ~2-3 years old) shuts itself down after a few minutes and gives me two red error lights (Overheat, not RROD) + subsequent "your console was shut down to protect itself" message on startup.
Environment: Equipment tower, clean with acceptable ventilation.
Steps taken: Checked for dust/obstructions on outside of case. Checked fans (working). Disassembled unit (PITA ><) and cleaned interior - surprisingly dust-free. Ran baseline test with hard drive removed, no disc in drive, open case, idling at the menu screen and still got crash within ~5 minutes.
Steps NOT taken: Did not replace any parts, did not remove heatsinks and reapply thermal paste.

Question: Where to proceed from here? I use the system regularly, but I can live without it for a short time if sending it off for repair (~100-150$ from Microsoft, not sure on third parties) is the best option. I can start purchasing parts/paste if folks have had success with that in the past. I can just buy a new system straight out, if consensus is these newfangled Elites and Slims are significantly nicer than the old Pro models to the tune of 200$.

Thanks for any help or horror/success stories you can offer! -Kisu, FFXI

Yeah, first stop was to check with Microsoft support and make sure that they wouldn't take care of it. Warranty ended over a year ago and since this was an overheat error rather than RROD it isn't covered under their 3-year-extension.

Thanks for the input. I may just take a crack at it - I don't have limitless hardware confidence, but since thermal compound and a bit of hardware is a 20$ rather than 200$ fix, might give it a shot first. I'm encouraged that it turns on and runs fine, for a very short time, so most of the parts are good.