Sometimes, when I click on something I get a double click and when I drag/drop an object, the operation fails as if I had unpressed the LMB before destination. If I press a little harder, the problem goes away, so it is the mouse (LMB), but it's a high end model (Alienware/Logitech) and I would prefer to repair it than change it.
I literally just fixed this in my mouse this past week. The problem is as Vurbal said. It's in the micro-switch. There's a very thin strip of metal that is bent in such a way that when you press down on the mouse button, it clicks down. Over time, it gets a bit bent out of shape and the click isn't as reliable, resulting in double clicks or clicks canceling even though you're still holding the button down.
You can try to fix it by opening up the switch and bending that little metal strip. Or you can just buy a new switch and either open it up and replace the little strip or replace the entire strip with some soldering.
I did it both ways. I have two Logitech M570 mice that both exhibited this click misbehavior. One started almost immediately after I bought it (as a replacement for a previous Logitech mouse with the same behavior!) so Logitech sent me a new one for free and didn't ask me to return the defective one. That was a couple of years ago. Lately the replacement started to have the same problem, so instead of buying a brand new mouse for $60 (or whatever) I decided to repair it for $0.60. I bought some micro-switches, but didn't have any soldering gear, so I just swapped out the thin strip of metal and my mouse is working fine. Then I decided to repair the older mouse which was essentially brand new and unused since I bought it, but this time I bought a soldering iron and solder wick (also known as desoldering braid) and fully replaced the micro-switch on it. Now I have two mice that both work better than they did when they were brand new. (c:
You can find some micro-switches for pretty cheap here: OMRON D2FC-F7N
You can also search on eBay.
(Special thanks to Edvard for giving me most of this information in the IRC channel a couple of weeks ago)