I haven't done heroics in a few weeks but unless they slipped in a hotfix after 3.09 none of the Gundrak bosses are leashed, you can run around all over the place with them. I'll be running them again this weekend or next week in marathons to get my DK geared up so will letcha know.

Eck has a hard enrage of something like a minute, I was once trying to get everyone sprayed for the achievement (kill last boss with eck gunk still on you) and he suddenly enraged after like a minute and 1 shotted everyone. So yeah, you don't want to waste time on that boss, just go all out from the get go.