You may have noticed through Disk 3, that something is not going so well with Mognet. A lot of people are not getting letters. Eventually you will see Artimecian, who claims there is nothing wrong. This is actually the beginning of a small side quest, to get the Mognet running again.
When you get the flying ability for Choco, head for the long island north of Madain Sari. Here you will find a crack on the northern face of the mountain. Use a Dead Pepper, and head inside. Once you are inside, speak to Artimecian. (The one in the blue coat.) He will explain that he used "it" on his fur to make it soft and shiny, but now there is none left to grease the machine. After the gears began to grind, it just stopped. This is all he tells you too. You will have to leave, not knowing what "it" is, or where to go to next.
I went back to the first place I saw Artimecian...the city of Alexandria.

Before we begin, check your Key Items. If you have any Kupo Nuts, take them to the moogles in Gizamaluke's Grotto. Each time you deliver a letter, and have no Kupo Nuts, you will be given one. Take each of them to the moogle family between deliveries. You will get various items, as well as the final Aloha Shirt.

	Here is the beginning. Ask Mog about Mognet, and he will have you deliver a letter to Alta.
	Alta is in Burmecia, and he has a letter for Mogryo.
	Mogryo is in the Black Mage Village, by the Chocobo house. He will have a letter for Kumool.
	Kumool can be found in Ipsen's Castle. He will ask that you deliver a letter to Mois.
	Mois has moved from the Ice Cavern on Disk 4. He will be located in front of Fossil Roo. Be sure to have Quina in your party, to get to the entrance. He will ask you to deliver a letter to Noggy.
	Noggy is in Daguerro on the second floor. He will then ask you to deliver a letter to Kupo.
	Deliver this final letter to Kupo, and you will learn the name of "it" is Superslick. Of course Mog has no clue as to whom might have it. But you know someone in Alexandria has it. On Disk 4, it is very easy to find, since half the city is gone.

Ask around, and eventually you will find Ruby in her theater. She will have the item you seek, and gladly hands it over to you. Take the Superslick back to Mognet, and hand it over to Artimecian. He will then fly over to the machine, and get it going again. Once the letters begin to flow, you will be rewarded with a Protect Ring. It may not seem like a whole lot, but you really didn't do anything major either.