I wish I knew about the knees the first time around (back in March). I blasted away at that thing with no effect, so I figured the 3 grav lifts in the building were the clue. I used the grav lift to jump off the top of the center building and onto the Scrab's back. It took me about 10 deaths to get the lift placed correctly and time the jump right. Once I was on board it was easy to mop up the remaining brutes/grunts and blow the reactor. So much easier the second time when I just took out the knees on my way to completing Legendary. There was a post on here a while back of a guy who took it down with a Mongoose and a marine riding on back with the rocket launcher. THAT was amazing. Foster