PERC6i 740YX (3) RAID5 STS failure suggestion? advice :)

good morning-

We have 3 740YX in RAID5 on a PERC6i SAS RAID Controller with 1 drive failure (4 years old). 

I slimmed the network share down to 300gb -it is only used for documents and quickbooks... no need for SAS in the first place... ~5gb veem changes a day.

It is now being uploaded to crash plan but I am still considering rebuilding the RAID5.

Computer Model PowerEdge T310

Shipping Date 1/12/2012

341-6175 : PERC6i SAS RAID Controller Internal with Battery

740YX 3 HARD DRIVE, 1T, NL6, 7.2K, 3.5, S-MSKP

1- Would you buy 3 new drives and rebuild the array? Or should I trash the old controller and just stay on crashplan? 

2- Can I get this ST1000NM0023 from cdw and replace the failed drive?

740YX 3 HARD DRIVE, 1T, NL6, 7.2K, 3.5, S-MSKP

Seagate Part# ST1000NM0001

www.cdw.com/.../2961609.aspx

We no longer carry Seagate Constellation ES ST1000NM0001 - hard drive - 1 TB - SAS-2 (ST1000NM0001),
but we found this replacement for you (ST1000NM0023).

Your ideas and expertise are always appreciated :).