Alan, John; your points are well taken and noted. There is no way that adding a fan will be the magic cure-all for older 5V boards! All I am trying to do is tip the odds, if ever so slightly. Preemptive if you will. What I know is hood units like F3/F7's with 5V boards seem to run noticeably warm, probably because there is limited open air space in those shells and lots of heat being generated. Things like E6/E8's, Dash 9's, SD-60/70/90's, not so much. There is acres of space in those longer shells and over-heating seems to be less of an issue as a result.
So my plan is to eventually add fan cooling to all the 5V F units on the roster. If none of them ever fails, there will be no way to know if the additional cooling made any difference or not, but who cares? And certainly if/when they do fail with something more serious than a cap or fet problem, it's time to move on, as many here have said. That's a given. 
