Is it worth it to zero-out unreadable (pending) sectors with dd on an old drive?

[lightheat]

Got this critical alert today:

Device: /dev/ada3, 16 Currently unreadable (pending) sectors

I've attached the SMART results of the last completed scan. I'm currently running a long scan to discover the LBA of first error for the pending sectors, which will complete tonight around midnight EDT. You'll notice that there were 3 SMART errors in the first 43 hours of this HDD's life, but that it has run for 38368 hours since then without error, until now. Drive was manufactured 2015-10-01.

Specs:

• E5-2640v2
• Supermicro X9SRH-7F (w/ onboard LSI 2308 hba)
• 2x 16 GB DDR3 RDIMMs
• Seasonic 80+ gold 550W PSU
• 2x SanDisk U100 16 GB SSDs in RAID1
• 8x HGST Deskstar NAS 6 TB (RAIDZ2)
• 2x Athena Power 5 in 3 HDD cage/backplane
• iStarUSA D-400-6 chassis
• FreeNAS 11.1-U6 (caffd76fa)

Questions:

1. Would it be worth it to run dd to zero-out the pending sectors and buy some time, or would I be better off replacing the drive right away?
2. Since the drive is AF, I assume I need to divide the LBA_of_first_error by 8 to get the physical block address. If the logical block address of the first error is, for example, 800000, would this be the proper format for the dd command?
   dd if=/dev/zero of=/dev/ada3 bs=4096 count=1 seek=100000
3. Taking into account #2 (i.e. dividing the LBA by 8), this is the guide I planned on following. Is it safe?
4. Is there else anything I should know?

Thank you for taking the time.