vinegar would be perfect for the job. Good, cheap, plain white vinegar. What I find works really well is to soak an old towel or some rags with the vinegar and lay them over the area that needs cleaning. Leave the rags there for as long as you can stand to wait. If you can leave them there for a couple hours they'll really go to work for you. Get an abraisvie scrub brush or a plastic scouring pad to losen any hard water deposits that might still be lingering. They'll most likely come off easily since the vinegar has had the time to work on them.
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