I would just like to echo what "Arkansas RV" and his "seasoned mechanics" said about old and rotted-out fuel lines.
I read about some owners who elected to replace their fuel lines, but to my knowledge these owners did NOT upgrade to a FASS or Airdog electric fuel pump. That said, I can only conclude the following:
* If there is any truth and value to replacing older pre-2003 fuel lines, due to a different rubber composition, it would have to do with these fuel lines being able to "suck-in" air... which would then render the CAPS Low Pressure Gear Pump with less than the -5PSI needed to pump enough fuel to the CAPS High Pressure Gear Pump.
Air = Bad
FASS or AirDog = GOOD!
* Now if you take that same fuel line and run an AirDog or FASS electric fuel pump, which filters out any air that may get induced by an old fuel line or leaking gasket, this point is now mute, because both of these pumps are designed to remove air in the fuel and return that air to the tank.
My guess is that these owners who replaced their old fuel lines did so on the advice of their mechanic who no doubt charged them big bucks to repair.
The owner then leaves the shop thinking they got his/her monies worth, because the engine is now running right. However, I would argue the better solution (for less money) would be to upgrade to either the FASS or AirDog electric fuel pump.
So, IMO, if there is any truth to air getting sucked into older fuel lines, to the best of my knowledge, not one of these owners reported fuel leaking out of those same, old fuel lines.
That said, I would pay no attention to old fuel lines if you upgrade to a FASS or AirDog.
I would add, that the money you spend to upgrade to a FASS or AirDog is protect your CAPS injection pump and ECM from premature failure; which if you have been following my other posts, this repair cost me $9,500 at a Cummins dealer in 2017; and my mileage at the time was ~73,000 miles.
And just so you know, when your CAPS injection pump blows... 9x out of 10 you also blow your ECM because the suppression diode designed to protect the ECM from "transient spikes" is not enough to protect the ECM when the CAPS Stator goes "haywire!"
What irks me through my whole repair process is this: Not once did any Cummins or Freightliner mechanic tell me about upgrading to FASS. And it was another 10,000 miles later I began to experience fuel delivery problems. (Short story: IT WAS NOT DUE TO BAD FUEL OR CLOGGED FUEL FILTERS.)
What a shame! ...And that my friends is why IRV2.com is so awesome! ...Because now you know what you need to do in order to avoid a premature CAPS & ECM failure.
To say it another way: With a FASS or AirDog upgrade pump, there is no reason your CAPS and ECM will NOT last the life of your engine!
The reason for this is that both FASS or AirDog filter out the air in the fuel lines and provide positive fuel pressure to your CAPS injection pump -- keeping it lubricated and cool -- especially under load!!!
The major difference between FASS-TS & Airdog-II-4G pumps has to do with the way they are designed, but from an installation point of view your decision to choose one over the other might have more to do with your willingness to run a dedicated FASS fuel return line to the tank, which the AirDog-4G does not need, according to "Arkansas RV." ...And I believe him. He is reporting great results.
On the other hand, FASS may do a better job filtering fuel over-and-over, because it is constantly pumping 95GPH and returning unused fuel to you tank.
FASS calls this "Fuel Polishing," but how do I really know if this is a benefit not? ...I guess I have to believe more fuel being filtered, more often, is better, but is it really?
The AirDog-4G is a demand flow pump and will not return very much fuel to the tank. ...But after 10,000 miles who cares! ...Because I would think by then you have a very clean tank, but maybe not? ...These bio-fuels contain a lot of "crap" for lack of knowing what I should call it.
My fuel tanks were in bad shape and I believe I had an algae problem. So maybe in these cases the FASS pump will be a better choice? You decide. I'm happy with my FASS-TS pump, and it really was not a big-whoop to install a fuel return line to the filler-neck of my tank. (See my thread on this subject.)
On the other hand, "Arkansas RV" went with the AirDog-II-4G pump and he "T'd" into the CAPS fuel return line without any difficulty. So it's a coin toss at this point as to which pump might be better than the other. IMO.