When you run the preclear, the two "Current pending sector" should go to zero and not increase if the disc has any hope. Since this is a Western digital drive, if the two sectors pending reallocation are readable the "Current pending sector" count and the "Reallocated event count" will both be zero after the preclear. If the two sectors pending relocation are not readable, then your "Current pending sector" count should go to zero and your "Reallocated event count" should go to two.
IMHO if either of the above happen and you run three preclears and another extended SMART test than you could probably use the disc again. However, if the extended SMART test fails or your "Current pending sector" count or "Reallocated event count" goes higher than two, than the disc should be discarded.
One of my 8TB REDs with less than a year's worth of hours suddenly had two pending sectors. I replaced the drive and rebuild the array (in your case without parity all you can do is try and copy the data first). I ran a preclear and then "Current pending sector" count and "Reallocated event count" both read zero after. I then ran another two preclears and then an extended SMART test. No new "Current pending sector" count or "Reallocated event count" so I then returned the disc to its original location in the array. The drive has worked flawlessly for many months since then.
Best,
craigr