Yeah, the whole walker part of this quest is ****ed. It took me 7 tries just to make it to the Zakuul Walker, and another 4 to beat him. Best advice I can give is to bombard him with both the Fury Mortars, and your walker's basic attack. The stomp no longer works. When he pops his shield, and summons the rocket ******e adds, use a grav mine, pop your 3-second shield, and kill the adds as fast as you can. When I fought him, he only does the shield/add phase twice, so if you make it past the second phase, you should just be able to spam him to death with Fury Mortars, and the basic attack. Hope this helps!