The recipe for the Crusader Enchant drops from two specific mobs in Eastern Plaguelands, as of Cata.
https://wowpedia.fandom.com/wiki/Scarlet_Archmage
https://wowpedia.fandom.com/wiki/Scarlet_Praetorian
What’s the problem? These NPC’s disappear once you complete a quest that’s very early into the Brotherhood of the Light quest chain.
https://wowpedia.fandom.com/wiki/Soft_Landing
Players are not warned that the only way to farm the recipe will disappear after this quest. Once you complete it, if you want the recipe, you will have to farm it on an alt or a Class Trial. The more alts you have who already did the questline, the worse it is.
I’m strongly against phasing locking you out of content like this. I would love it if Blizzard put the recipe on other mobs’ loot tables as well. They can put it on the loot table of the Scarlet mobs in Stratholme, for example.
And, I don’t know where else to put this, but for the new Secrets of Naxxramas, you have to complete a quest given by Archmage Angela Dosantos, who disappears after you complete the Brotherhood of the Light questline. You have to talk to her on an alt if you already did the questline. The fact that Blizzard made it like this shows that they didn’t consider the phasing issue once again. Imo, they should add a version of her at Light’s Hope Chapel as well. They could also let you talk to the version of her in Stratholme, which appears after you kill Lorde Aurius Rivendare. Here’s her quest.
https://www.wowhead.com/quest=76265/the-dread-citadel-naxxramas