Try SpinRite.
Well worth its purchase price, if for no other reason than to watch all the crazy output it displays. Apparently, it goes over the drive with an ultra fine tooth comb at a very low level. It worked well for a drive of mine which only partially survived a power surge.

Be sure to run it in the computer the drive was originally hooked up to. And be sure to let it run a long long long time. So, you main machine will be busy probably for days, but you may have good results. (or you can pause and restart it, but I'd rather let it run and run).