there are many causes of RROD

1) GPU overheated and need xclamp fix and overheat to reball chip.
2) Ram chips over heating causing same error add heatsinks
3) ana scaler chip overheated and pulled from board, needs heat gun trick then add a heatsink

These are the main causes of the RROD fix them all and you should have a long lasting xbox.. But and this is a BIG BUT! none of these i would say could permantly fix your xbox but in my experiance i fix all and haven't had any come backs as yet. But i guess it just depends on how well you fix it and how good you are at doing it.

Good luck and hope this has been some help!