If you have been lucky enough to still have your laptop running after spilling juice in it Twice, I would say you are a very lucky person.
As far as the bad sectors on your hard drive, I would recommend using the manufacturers hard drive testing utility to check the drive for full functionality. In my experience, once the drive has experienced bad sectors, 99 chances out of 100 even if they are remapped using the testing utility, the drive will continue to show more and more bad sectors. At this point it would be best to replace the hard drive and reinstall the operating system.
I would also recommend checking whether or not your laptop will recognize a 500gb hard drive before purchasing such a large drive.
This link will provide you with links to the manufacturers hard drive testing utilities. - > Link.
Hope this helps,