Given the fact that the ones from amazon go for 26 bucks a pop, I'd go with the safer option and get it from logi directly instead of asian re-sellers.
You get manufacturer guarantee, it's not worth saving 2-3 bucks on ebay re-sellers
What are you doing with your mice? Does this happen to you with all mice or is it specific to g100? I had lots of mice, both expensive and cheap, and not once did my left buton fail.
You can thank the general decline in quality of Logitech products over the past several years. Not sure how they're doing financially, maybe they have to cut costs. But, I sure would like to know where the company that built the wingman mouse or mx300 went. The only thing Logitech really has going for it in at least a couple areas is price. But that won't always be the case.
Thats a shame. For the last 6 or 7 years i was mostly using some cheap logitech ps2 mouse that I got for free when I bought my old pc. I removed the bottom sticker from it a long time ago so I dont know the model name, but it looks just like g1/mx300 only all white. Every thing about it was perfect until I started playing with a bit lower sensitivity. It has terrible polling speed and now it skips when I do fast turns :(