Determining problem: lock button or power button flex cable

Hey everyone, I searched for the answer but couldn't find it if it is already present on the site.

1. My lock button has been having problems locking my phone.

-Sometimes I must click it 2-5 times to get the screen to lock and go into sleep mode.

-It does physically click, I can feel it. Although, the other day it didn't click at all and wouldn't work at all. It seems to have improved some and now it will click again, but as I said, sometimes it takes 2-5 clicks just to get it to lock.

-The proximity sensor still works.

So what I am asking is: Do I need to replace the physical lock button, or the proximity light sensor and power button flex cable ribbon? Or both? How can I tell which is having issues specifically?

I appreciate the advice mates.