Almost all cast iron can be saved, and brought back to near new condition in a few steps.
I have been hunting for a large skillet, like my dads, that I grew up with, but frankly, too cheap to pay some ridiculous amount for a new one. So, wifey (very soon) found an old one in the thrift store, sent me pics while I was at work, and I said grab it. For $35.
The first thing you need to do is get rid of the old, probably mistreated seasoning. Seasonings can be done wrong, or go bad with neglect. Too cool of a temp while seasoning, and it can just rub off.
If you have a self clean oven, this is the easiest. Throw the pan in the oven during the cleaning cycle. Just like that, its back to its basic, iron looking pan. It may need a bit of light scraping to remove any flakes, but it's back to normal again.
Now its just like seasoning a new pan.
I use Crisco lard. Mostly because it has a high boiling temp. Some people dont realize that all oils are different, and have lower boiling temps than others. Olive oil is the worst. It will burn at anything over medium heat if left long enough, and ruin a good pan. Well, not ruin, because you just repeat step one!
Anyway, coat the entire pan in lard, handle, bottom, the works. Put something in the bottom of your oven to catch the drips.
I preheat the oven to about 450. I find it works well.
Put the pan in upside down on a rack, and leave it in there for an hour minimum.
Once again, Ill say too cool of a temp is no good.
And yes, your house is gonna stink for a bit as the lard cooks itself onto the pan.
After an hour, let it cool, and repeat the process again.
Twice is usually good enough, but sometimes a third might be necessary.
After youve done this, and before you put it away, give it a light rub with more lard, or oil. Something to keep any moisture from setting in.
Now to keep it well seasoned is the trick.
After every use, a tablespoon or so of good oil or lard in the pan, and put it on the stove top at about medium heat until it JUST starts to smoke. Turn it off and give it a quick wipe and let it cool.
This should be done AFTER EVERY WASHING!
Your pan will get nothing but better. If you find it not working well, start all over.