G'Day Mate, the lifterplate is as fragile as f*ck, and there must be amillion busted ones out there, I've got three or four myself. You need to tighten the 4 6mm screws evenly, or you'll keep busting them. I've seen some bodges with washers etc, but don't recommend it, I'd hate for a part like that to disappear into your transmission!
The clutch itself needs to be assembled carefully, making sure all the "splines" are lined up perfectly, or that clutch will never work well. Also, on later models, like yours, the fibre plates all have to go in with the grooves pointing in the same direction, as per the diagram in the manual, as they're designed to move oil around the clutch assembly. Cheers, Terry.
