RAID 5 created with Disc Utility - how to replace a bad HDD?

Hi,

I have a 5x6TB RAID5 array that's run great for 2.5 years. Suddenly, one of the HDDs went bad (I think) and the bay light is flashing red (meaning it's bad). I created this RAID using Disc Utility. The manual for the array said I just replace the bad HDD but that's if I had used the hardware RAID included with the device. (yeah, stupid me)

The RAID won't mount but it shows up as an item in Disc Utility. How can I replace the bad disc and get back my RAID5 array?

Any help?