I've been using triple thick for over 10 years, and I've never had an issue. Follow the instructions on the can.

For small areas, you can simply seal that section only.

Nino, i too have been using triple thick for 10 years and only have had a problem on a BK bg.

Doing some reading and research apparently around this era early 80's Williiams was trying to save coin where they could and one place was using inferior inks and thinner glass on their bg's. The dual playfield games pins especially.