So basically using the seed "Mojang" I have found this.
These four veins are very very close together.
I don't mean to boast rather i would like to show you how to get here so if you'll tag along through all of my confusing instructions.
This should be your spawn.
Now if you cross the river over to my house (I know it's not that great.)and come to these coordinates.
I dug a two by two down for a bit and then I hit a sandstone block or something that started dropping sand (I replaced it.)
I then fell into a cavern leaving me with options of straight,left or right.
I chose anything but left (If you want the diamond go LEFT.) straight doesn't go very far,right on the other hand goes a medium distance. (watch out theres holes)
When you go left there is a circular room and if you go straight there is another thing you can go down.(Again if you want the diamond go Left.)
I made a path going down.
Now if you went down the water and go right there will be a short little cave go through it.
You'll know that your in the right place if theres iron to your left.
Note:It's on my right because i'm walking backwards.
When your out of this small cavern it should look like this if you turn around.
There should be a dividing wall go to the left of that.
There will be a hole you should make stairs down the hole.
If you make the stairs like i did you can go under the stairs and then go left there will be another small cavern go down it.
Then there will be many ways in which you can go your, going to go this way.
And follow the cavern, as you go you will see a big block of gravel.
Go left, you will see something looking like this.
Follow that cavern, to your right will be find two and three.
Further two your right will be find four entrapped in stone i believe you can see the top.
To your left there will be water and by the water is find one.
All in all this is 27 diamond if i counted correctly, please feel free to leave feedback.
Sorry if these instructions were overly simplistic or utterly confusing.
Hopefully this gives you all many 's , I hope this helped someone.
Ive found it using just my hands some things are different as i was exploring and i mined stuff but you should be able to locate all of them, four out of site three out of two and one after you dig the coal.
Please comment as i spent a bit on this and wanted to share with everyone.
im trying this map out on peaceful, just seeing if I can manage to find it all.
Maybe its just me, but i cant find that exact point you dug down into, the massive hole i fall into has only 2 directions. so i take both, and in one.. im at cords x:27 y:14 x:42 and i found a mob spawner right near some lava. so i went and mined the mossy, and udnerneath the mossy there were 2 more diamonds.
Be careful if you mine the mossy out there though, one has nothing under it, and lands right next to lava on a gravel block. scared me to death haha