By chance I found out something rather strange:
Up to now I had set Backup retention to Custom backup retention 7D:U,4W:1W,36M:1M on PC1 and also on PC2.
I changed this to Keep all backups on PC2 only.
Now database Repair on PC2 worked without any problem.
So I do not have to perform this delete procedure.
I´m happy (for the moment)