[OK many thanks for your help. Some results to follow.
What about some software, as mentioned above, to at least give you a preliminary look at what the condition is?
There's SSDlife Free 2.5.82, that's free (obviously). It will show a basic condition report. Another better option is Hard Disk Sentinel. I'm not sure what the price is, but they might have a 'try before you buy' option. They were giving it away for a day the other week at no charge, so I was able to grab a copy. It is impressive.
SSD Life (Free)
Hard Disk Sentinel