"If Cameron's power supply was damaged, John would have cancer too. Even so, if she believed it could be leaking radiation, why the hell would she let him touch it?"

I think it was about trust really. She knew it wasn't leaking, but John needed to see for himself.

"Since we just had the Jesse story wherein she spent all season trying to win future war by messing with John's love life, I really hope we're not going to find out Cameron was doing the same. But at this point it's looking that way."

I'm not buying the manipulation angle. Yes, at some point Cameron wanted to get closer to John and was manipulating his feelings. But that last scene I read quiet differently.

First, she begins by telling him she a murdering terminator and that she might kill him someday. If she so wanted him to fall for her wouldn't she be telling him the exact opposite?

Second, she actually breaks the moment by telling John they need to go. She didn't let him take it further, which could have happened.

No, I think it's like she tells Sarah. John has to be alone. The way he cares for people, Cameron herself included, is dangerous as she sees it. IMO, she leaves in part because she doesn't trust herself with him fully.