My old MX-518 have started acting up a bit. Quite often it double clicks even if I just click once and it's quite annoying at times. I guess it's just started to show it's age, it's worn out. Might try to open and clean it up and see if that helps but I guess it's the micro switch that's just close to getting finished. I've loved this mouse, I've been so happy with it I've never considered getting a new one. Lots of mice I've tried in stores doesn't feel as comfortable for my big hands and my thumb keeps pressing the side buttons, something that just haven't happened many times at all with this one. So, I want suggestions for a replacement that's fairly similar in design and quality without being to darn expensive.