The Roadie is, of course, correct. Nitrogen molecules are within 10% of the size of oxygen molecules. (They are side by side on the elements table.)
This hoax has been perpetuated by the suppliers of nitrogen filling stations and nitrogen retailers for many years and has absolutely ZERO basis in science. Air is already 78% nitrogen, and the most one can get from a filling station is about 98% nitrogen.
Think about it ... if nitrogen molecules actually leaked less than oxygen molecules, then given time, the only air left in your tires would eventually be 100% nitrogen, and you get it for free. Anyone who tries to tell you nitrogen molecules leak less than air has no concept of the size of a molecule.
Most race teams use plain old air, and if they use nitrogen, it is because it is clean, dry and delivered straight to their pits in clean cylinders. The myth about NASCAR and drag racers started because nitrogen doesn't expand as much as air with large temperature changes, but one would need large volumes and HUGE temperature changes.
This is why airlines use nitrogen in airline tires. Wheel wells are tight fits and tires can go from minus 200 degrees at altitude to plus 300 degrees instantly upon touching down. This means that a tire accidentally filled with air might not retract properly after a balked landing.
Plus, in an airline fire, if a tire bursts, air will add oxygen to the flames but nitrogen will not.
As for fuel filters being the most oversold item on the shelves, fuel filters have rarely solved any problems. Yes, they need to be changed according to the manufacturer's schedules but unless one gets a very rare load of bad gas, they don't need to be changed anywhere near as often as some people recommend.
I have been a member of this and other forums for many years, and when one has a drivability problem, it is very common to hear, "I was told to try changing the fuel filter." In all those years, I have only heard of one instance where it helped.
If I did a lot of traveling in remote areas or was driving through areas where the quality of the gas may be questionable, I would certainly carry an extra one with me, not expecting I would need it so much as knowing the consequences of a plugged filter.