Well, if I were you I'd just purchase another new rotor.
You asked how to diagnose bad caliper or rubber line, here's how.

Remove rubber line from the caliper end. Compress caliper. If the caliper fails to compress, than that's your problem. If the caliper compresses without a problem, than your brake line is your problem. You won't be able to tell anything, if you don't remove the line off of the caliper end first.

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[SIGPIC][/SIGPIC]