Aye, Cthulku has it down perfectly.  If only one lock has the lodestone, only that lock can keep repairing the three items with keep breaking down.  If two locks have the lodestone it just makes it easier...

There is a very very good writeup on the quest chain at [url=http://wowmb.net/index.php?page=Dreadsteed]wowmb.net [/url]which covers everything very very well.  According to this site you save up to 250gp by not purchasing those last three items.  I remember the day when locks with the items would charge 20gp+ to help other locks!  Anyway, notes from wowmb.net:

Through out the quest line, you will be required to hand in certain components to move forward. Some of the items you will have to collect yourself from the NPC's, however most are obtained via some form of profession, so be sure to check if any friends or guildmates can help with what you can not collect yourself. Below is a list of all the items required in the order you need to hand them in:

[i:a3c0ca45a6]Material Collections[/i:a3c0ca45a6]
35 x Black Dragonscales
10 x Elixirs of Shadow Power
6 x Large Brilliant Shards
25 x Dark Iron Ore
3 x Arcanite Bars

[i:a3c0ca45a6]The Xorothian Glyphs[/i:a3c0ca45a6]
1 Shadowy Potion 
Xorothian Stardust 

[i:a3c0ca45a6]The Ritual*[/i:a3c0ca45a6]
J'eevee's Jar 
Black Lodestone 
Xorothian Glyphs 

* The three items used in the end stage of the quest are the only items you don't need to purchase if you know someone who already has them. For more detail on how to obtain these items, please see the relevant section of the quest below.

PS:  Why do these signature things keep breaking down?!  /scream