We have an old claw tub (50+ years old) in our apartment. In an attempt to clean and brighten it up we used bleach!
For the bleach stain on the old porcelain tub, I would try using either "Barkeeper's Friend" or Zud, both are recommended by the porcelain enamel industry for cleaning everything from porcelain sinks to school chalkboards and whiteboards. Works on copper bottom pots too.
I tried the baking soda/peroxide blend on my clorox stain in the tub and voila, no more stain! Thank you!
Clorox 2 was the answer for me! I made the same mistake of using bleach on an old porcelain tub and Clorox 2 liquid worked like a miracle! I didn't even have to scrub - just poured the Clorox 2 all over the tub, spread it around and let it sit for a little while and it removed all the brown stains like magic!
I used comet liquid spray bathroom cleaner on my claw tub. You let it sit. I am not sure about the bleach stains, but try the comet.