I had one rotor that, with all the suggestions above, just wouldn't come off. I put a large gear puller on it, pushing against the axle stub after removing the sheet metal cap. I didn't pull it off with the gear puller, just set up a decent amount of pull, then whanged away with a 2-pound hammer on the outside edge of the rotor. It finally popped loose and came off by hand.

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There is a very fine line between "hobby" and "mental illness."
FrankenBenz: '87 560SEC with an '02 cammed LS6 and custom 4L60E.
Bling: '87 560SEC, ported/polished, lowered
Lisa: '87 560SEL, lowered