A while ago, I repaired the heating wire on a VIVIO rear defogger.
I used this conductive pen.
https://www.amazon.co.jp/dp/B0CPYS8F...fed_asin_title
I hadn't been able to check it until today, but yesterday I went out in the rain, so the room was damp and there was condensation this morning. One of the many heating wires was scraped and didn't work, but it seems to have been repaired successfully.