Failed IDE Diagnostics with return code 7 then later passed it just fine

Had a customers machine with unmountable boot volume when I tried to boot it up. Ran the Dell IDE drive diagnostics and ended up with return code 7. Figured, ok the drive is cooked which is normally the case with a return code 7. Took machine with me and when I got it home I tried firing it up again just for kicks and it booted up and ran fine. I then decided to run a Check Disk from within windows. I included the scanning for and repair bad sectors option. The scan completed successfully and completely. Thought it was odd everything now seemed fine so I reran the IDE Drive Diagnostics to see if it would still kick out a return code 7 and it didn't. It passed just fine. I've booted it a handful of times since then and it seems fine. Would you trust the hard drive at this point? Its a much older Optiplex 170 but the hard drive itself is only a couple of years old. Just wanted to get another opinion.

Thanks in advance,

Adam