Quality of Brick, Modified 1 x 1 with Headlight over time
I just got a call from LEGO Support. I can't repeat it word for word, but (translating to English) it was like:


  Over the last decade manufacturing process of this brick has undergone many improvements that have improved its durability. You shouldn't encounter any problems with new ones if you will buy them, and if you will have problems in two years after buy, we will replace them free of charge. Sadly, we can't replace parts older than 2 years for you for free.


Two years of play is quite a long time, so it seems they are pretty confident about quality now.