... or an intermittent power failure due to improper cable crimping....

... or incipient CS4231A failure (rare)...

Most times I have seen drive failure, the drive simply fails to start spinning ("Click of Death") or the disk spins up and the heads fail to pull in ("Spinning Silence"). For a drive to become "intermittent" is unlikely - it either works, or it doesn't.

I think he should (as you say) dismantle, look at the headers on the board, and carefully check the crimping on the drive cable.