I agree with Mr Vic - in this situation, I would follow Occam's Razor and initially assume that the simplest explanation is the most likely explanation, which is that the pen needs cleaning (badly). If you don't have an ultrasonic cleaner (ah yes, another tool to buy), the best approach would be to soak the section in a container of water for several hours, possibly overnight. Adding a little household ammonia could help*. After soaking, use a converter or ear syringe to force warm water through the section and nib - repeat until the water coming out of the nib is clear. That should clean out any dried ink inside the section and nib.
It may also be necessary to 'floss out' the gap between the tines of the nib using a small bit of brass shim. This has to be done carefully because it can also change the alignment of the tines and make the problem worse.
I am puzzled by the statement that the person who owns the pen claims that it was never able to write. If that is the case, why did he wait many years to complain about the problem? There's a reason why manufacturers put time limits on warranties.
Unfortunately, it may be very difficult to find a replacement section for a pen that is many years old - the section screws into the body, and also is captured in a 'snap' sleeve inside the cap - so there are two critical items that would have to match for a substitute section to work. Pen kits aren't made to any known standard other than possibly the 'international standard' nipple dimensions for the cartridge/converter, and manufacturers can redesign their kits whenever they are so inclined.
* There are numerous discussions on the FPN site about pen flush formulas. Commercial pen flush solutions contain water (typically distilled water, but RO water should also be fine - just avoid tap water with a high mineral content), ammonia, and some kind of surfactant (which is a chemical that breaks down the surface tension of water). Component ratios vary - the general consensus on FPN seems to be that the solution normally should contain no more than 10% ordinary household ammonia although some people use a 'hot' solution that is up to 50% ammonia to address particularly desperate situations. The usual sufactant is dishwashing detergent in minute amounts (measured in drops), but you will also see formulas that suggest using PhotoFlo, the darkroom concentrate sold by Kodak for the final rinse when processing film. Kodak recommends using a ratio of 200 parts water with one part PhotoFlo. In my experience in darkroom work, that's a bit strong; I always doubled the amount of water when mixing a working solution of PhotoFlo.
