Since I have no need of a 4 disk NAS any longer, rather than replace the one disk that is nearing failure I’ve decided to switch to a basic setup without RAID. All disks are 6 years old so I could face having to replace them all to maintain my current RAID level. I spent this morning backing up configs and info. First thing tomorrow I’ll nuke the current config and start afresh. I’ll also clean all the dust out of it.