As I have been put back into the CL spot for clerics for the time being, I am going to copy choco and post what is needed to a core cleric in our guild.
All of these requirements are for those that are not one of the main tanks. Main tanks are the best tanks in the guild, so if you wish to be one you must pass Lealoo and/or Warks in both gear and skill.
Multiple Roles
You must be able to have AT LEAST three healing builds and AT LEAST one DPS build.
More specifically you must be able to effectively play Warden, Defiler and a tank healing soul of your choice. If you have both puri and sent even better. Warden and Defiler however have more specific requirements to them.
For Warden you must be able to keep the raid alive while keeping 5 stacks of Dangers of the Deep up. I can tell who is and is not doing this by your DPS.
For Defiler you must be able to pull at least 5k ST DPS in addition to any CDs or burst healing needed.
Mechanics
This is the same for everyone. If you are repeatedly dying to mechanics you can not be a core raider. If you improve you will be eligible for a CR spot again.
Hit Requirement
To be a Core Cleric you must have AT LEAST 508 hit unruned, no exceptions.
Damage
Along with meeting the requirements for healing you must also meet the requirements for DPS.
To be a Core Cleric you MUST be able to pull a minimum of 12K ST DPS on the dummy and maintain that in a raid. For AoE specs (if asked to be in one) you must be able to pull a minimum of 18K DPS.