G502 left button needs to be pressed further before "clicking"

Sounds like the switch in the mouse is wearing out. In theory you can get replacement switches, there is actually a whole community behind modifying these mice with different switches and lightening them, however you do need to know how to solder as the switches are soldered onto the PCB in the mouse. You should be able to follow the scroll wheel replacement guide here on iFixit to get the PCB out if you want to attempt to fix it. As for finding the specific switches your mouse needs, the r/MouseReview community on Reddit should be able to help you figure out what kind you need, the guys over there are kinda wizards at this stuff and have helped me in the past.