RRODs can sometimes be solved by reflowing the GPU AFAIK. Google / YouTube it. Basically, XBOX gets too hot and the solder melts, so the connections to your GPU are lost, causing RROD. To fix, it needs to be re-heated to the melting point for the solder so that the connections are active again.
This is why some people can temporarily fix an RROD by wrapping a towel around their XBOX and leaving it overnight. It causes enough heat to re-melt the solder around the GPU and make the connections again.
BTW, ofc it would make sense, after you re-flow your solder, to try to find a way to mod your XBOX so it doesn't overheat again. Extra fans, IDK. Google it.