An access time of 500ms corresponds to 60 revolutions at 7200 RPM. That’s a lot of retries.
Manufacturer’s tools such as DLG do not appear to be too concerned with how long it takes to read a sector. They’re more concerned with whether it is readable at all. I suspect that DLG will give a passing grade to all your “slow” sectors.
Instead I would perform a full surface scan with tools such as HDDScan (Windows) or MHDD (DOS).
