Can someone help me with my E73 error?

My xbox has had the red ring of death before and I fixed it myself... temporarily. I cleaned it out, removed the old thermal past, applied new thermal paste, and reset it. (with the penny fix as well) To my misfortune, it has returned a few times since the first try. I have applied new thermal past a few more times since then. A few weeks ago I started to get the E73 error with one flashing red light in the 4th bottom right quadrant. I simply reset it by overheating the unit and it worked for a while. That is, until it started to E73 constantly. Being sick of the constant E73 errors, I took apart the xbox once again and smothered the gpu and cpu with thermal paste since the time before I had only applied a light coat and it didn't work. Now I have to reset (overheat) my xbox after every power on because of the E73 error. It works fine until I turn off my xbox after any amount of time the xbox has been powered on. After I turn it off, it just error codes again. When I overheat the console now, it doesn't get very hot and it hardly takes any time to cool off. What can I do? Buying a new xbox isn't really an option by the way. I think the console might have some kind of problem with heat recognition or overheat recognition, that is.