So how do I fix the stiff left button issue?

"1. unscrew both philips screws inside the battery compartment (the ones that are below the batteries). There are two more under the front glide-pads, these go off easily with a sharp knife. Now open up.

2. in the top cover, unscrew both remaining screws. Then release the blue part of the cover a bit by pressing the two latches in the middle. Now shift the whole blue cover forward (button pins must go past the plastic holding them back.

3. Look at the black plastic top cover. You will see the metal plate of the battery terminals. The part below the left button will be lifted a bit (or may already have moved down by all the handling so far. Push it flush with the plastic top, and put some superglue between metal and plastic to lock it in place.

4. reassemble. Done"

"If your left click is taking command properly it would be due to carbon inside left click button.

After using long time it creates problem.Simply open mouse like as shown at up side. Take a small drop of petrol or thinner into button and continuously click by finger and repeat it twice or thrice. Now leave your mouse for dry liquid. Screw your mouse and use it. It will work fine.

I have fixed many mouse like this in my home and friends."

"if it's really bothering you, like my apple keyboard was after a soda ended up on it.... WD40..... Depending on the cause of the problem, may fix it.

i used a significant amount, also cleaned the keys which are nice and white again, aluminum parts too..... WD40 is great....... it's not an oil per say......everyone uses it for that...... al thou it has a bit in it.....it sucks the moisture out of things and cleans.......in all cases I have used it for, is harmless to electronic components (maybe some types of rubber etc won't like it, haven't had a problem yet)."

I went to email Logitech support and they said I could get a 1-to-1 exchange from wherever I bought it from. So, I did just that, and managed to exchange it for a new one indeed. You'll need to have a reference number from Logitech.