Your data is worth more than the cost of a higher capacity hard drive. Always back up your data before upgrading either your operating system or applications. Salt water is corrosive. Make sure you get your computer to a reputable restoration expert quickly. Don't be tempted to dry it yourself.
Modern drives are very complex and circuit boards can be unique to that drive.
Don't be tempted to swap circuit boards as this can result in irreversible data loss. Viruses can cause all sorts of mayhem with your data. Make sure you use current anti-virus software and update it regularly. Employ a scrutiny procedure and check all incoming floppy disks, CD-ROMs and emails for viruses . Lots of companies religiously back up their data, but never test it, only discovering when data is lost that their backups are useless.