Logitech x-540 6 channels amplifier

Hi, I have a problem with mine and I see the same white pastes too. But I couldn't debunk which component is failing. Only the front left output is significantly lower in volume compared to the rest. Everything else works fine. I have a couple of photos that I took.

https://www.dropbox.com/sh/8yoxf69yxlhqlue/bBjmWARHF-

I appreciate it if anybody could help me deduce which is the failing component that i should replace.

Thank you