Address the problems in the order of priority.
1) Get the trans code that is flashing the OD light. Could be something simple, unrelated to a dying trans (MLPS comes to mind as a common CD4E failure).
2) You wouldn't be the first person to kill their trans by getting it flushed for the first time this late in its life. Of course, if you don't address the code first, you'll never know if it was why or not. Personally, I wouldn't risk flushing at this point, especially as a first course of action.
Does the O/D light flash a pattern (like the airbag light does during a fault)? By this, I mean 4 flashes, short pause, 5 flashes, long pause, (repeat until insane). That hypothetical example would be a "code 45", which can be looked up in a service manual and let you know what caused it.
Post the code and someone can look it up for you. That will give you a place to start. No sense in guessing if the computer wants to give you a hint.
