Healers and bards can stand right behind the wall in the corner area where he spawns and silence won't land. Didn't hit that hard even on the rogue/zerker that were tanking. Did take a bit as it has a lot of hp but fight was a joke with a single group and no real tank.
I just did this with my 72 bard, 72 sk, and 73 wizard none of which are overly geared. Took me a while to figure out how to position my characters and mercs, but it was easy after that. I went behind the wall from where npc is laying on the ground with my wizard and healer merc. I then had my dpsers and tanks (tank merc works best, doesn't seem to get knocked back) tank him in a way that the mob was behind the wall, but the tank wasn't. I then had my healer merc on efficient and it was easy. The mob doesnt hit too hard, just constantly silences. I ran a tank/melee/healer merc combo, all J1. Only have journeyman because of 16 days of anniversary, otherwise i would suggest running tank, healer healer and just take awhile to kill metala. If adds respawn theres only three or so that would add and theyre not a big deal at lvl 70. I thought this was easier than the previous step with the thief.
This mob was like the final epic fight for the bard 1.5, and I'm sure a lot of people have a lot of questions about him concerning how hard he is. Fear not, he's not hard at all. :)
First off, position Korach so that he's cornered. If the casters are behind a wall, they will not get hit by his AE. This is, however, primarily a melee fight. The silence goes off a lot, and the wizards in our raid complained they could barely get a nuke off. Melee dps is golden here.
How hard is he physically? 650k hitpoints and does a whopping 250dps (13k+ hp and 2200ac+ tank). You'll have more to worry about the repops around you than Metala Von Korach himself. =)
After reviewing my logs, I don't see any flurries or rampages.