I'm trying to trouble-shoot the leak in a (Crane 1971) toilet tank, but the water shut-off valve is unwilling to budge. (If it was ever shut off before, it might have been done only once or twice.) Do you have any suggestions on how to loosen it up without breaking it off? I tried a little W-D 40 with no luck, but maybe I wasn't aggressive enough. Thank you for your help.