Before I install another hard drive I need to know if it is possible that the Speedzter 5 is causing the hard drive failure?
What kind of failure? When I turn on the power to the box I hear buzzing and clicking, etc. When I leave it on 20 minutes or so the drive does show up on Seagates SeaTools for Windows but running the test it is able to repair some Bad LBA's but eventually is "Unable to repair."
Did you notice the product description, "5.25" IEEE 1394/ USB 2.0 External Enclosure with High-Performance IEEE 1394/ USB Bridge Adapter Built-in to convert
ATAPI CD-RW, DVD-R/RW, DVD-RAM into IEEE 1394/ USB Devices"
Your drives are probably overheating in that non-ventilated case which was only intended for occasional use Optical Drives with low heat dissapation needs. Did you ever look at the "SMART" data on how hot your disks were in there? Above about 40 degrees celisus, hard disk drives start to malfunction and fail much more quickly.
According to manufactures, the normal recommended working temperature of a hard disk is 35-40°С. Once it rises by just 10°С – from 40°С to 50°С, the safety of its work becomes more than two times less.
One of the worst enemies of hard disk drives is heat. Within a drive, the reliability of both the electronics and the mechanics (such as the spindle motor and actuator bearings) degrades as temperature rises. Running any disk drive at extreme temperatures for long periods of time is detrimental and can eventually lead to permanent data loss.