[Sneck]

Of all the failed pits that I have ever seen, there seems to be one common thing about them all, and that is that they were all drilled. You can tell quite easily by noticing how perfectly "round" the missing pit was, and the fact that it was the exact same size of a drill bit. Some had turned yellow like bee-poop, while others just came clean out. I notice the missing pits more on vertical glass, but have also seen this on car windshields as well. I have not noticed it on any my old repairs, I never drill unless it is absolutely necessary.

I think these old failed pits are happening due to extreme temperature changes too, but I also think the smooth walls of the drill hole aid in the old pit filler to slip out.

Sneck