I found a workaround to the problem of determining the cleartext filenames.
*Before* you delete the zero-byte files, back 'em up:
1) tar find .Private -size 0b | xargs tar -czvf zerofiles.tgz
2) Unmount your encrypted home
3a) Temporarily move the "good" files away:
mv .Private .Private-real
3b) and restore the "broken" ones:
tar xzvf zerofiles.tgz
4) remount your encrypted home
The files will not be usable, but at least you know their names
5a) Unmount your unusable encrypted home
5b) restore the "good" encrypted files:
mv .Private .Private-broken
mv .Private-real .Private
6) Remount and continue.
My last problem: I *still* have 5 files for which I get
the "Valid eCryptfs headers not found in file header region or xattr region"
error. Since I purged all -size 0b files (verified!) I'd like to know
how to track those ones down. Is there another find expression
that can nail those down ? Any other debugging option I could/should
enable to find these 5 files ?