Thanks Mike!
With the new 1.9.3 I finally was able to read a DVD that I was working on for months.
The error was still recognized as UNCORRECTABLE ERROR but this was not repeated several times instead it took just a minute longer to finish the MKV-file.
Yes, the disc had some scratches and trying to remove them made it even worse. It was always playable on a standalone player. The error was in the last 4 seconds so it was propably not caused by the tiny scratches