SOLVED Can't replace drive in GUI

[cods69]

Another update with a back story prelude.
I wanted to add another old laptop drive to this box so I could let the RRDTool reporting write to it instead of the main volume so during extended lapses in work (which could be days or even a week) the main volume drives could spin down.
Considering the current PSU (Silverstone ST45SF-G) was right on it's 14A limit for the 5v rail, I decided to literally squeeze in a SX500-LG so there was enough juice on tap for another drive. It's tight, but fits as long as you do some good cable management.
So nearly everything came out of the case. New SATA cables put in, new PSU, additional laptop drive, a cardboard divider to channel more air over the drives from the side fans, etc.
I only use the molex cable from the PSU (due to the DS380 backplane) then split it off with an adaptor for the extra SATA power connector.

When taking the old splitter off, I noticed something which could have been the cause of the problems from the start. A collapsed molex connector pin (the translucent case type) was only just making connection, which just happened to be the red 5v.
I'd missed it due to the double sided velcro covering it when cables were wrapped up and routed.

So everything is powered back up and not one single CAM status issue so far, nor any other issues to speak of, so far.
I'll give it a scrub and a serious caning over the next week and check back in.

 

[cods69]

Going to set this to solved as the machine is completely rock solid now.
The problem was definitely the molex connector and the flakiness of the CAM/drive dropout issues has completely vanished after replacements/corrections.
Even though I threw a few bucks away on a few drives, PSU and other bits, I'm pretty happy with the outcome.
Many many thanks to all who assisted and contributed here. Was a valuable exercise for my education and a reminder to check every weak point in a solution such as the NAS I built.
Thanks all.