From: Rabbi Akiva Eiger
To: Unknown recipient
A sofer in Märkisch-Friedland presented mezuzos whose scoring lines were very crooked, rendering the writing insufficiently adjacent to the sirtut. Rabbi Akiva Eiger invalidated them and ruled that adding new scoring lines after the writing is complete does not remedy the defect, deriving this from the Gemara in Menachos and the language of the Rambam and Shulchan Aruch. A secondary question whether scoring with non-permanent tin before writing, followed by reed scoring after writing, might be valid was left as tzarich iyun.
Source: Shu"t Rabbi Akiva Eiger §50