Yamaha RX-V663BL cursed

[Sling]

I Purchased it a couple years ago and all it has given is a headache Left front channel stopped working 7 months ago.
When I plug in left channel works for short time then stops so I took it in for Bestbuy service.
It came back from service they said left channel connector solder broke so they re-soldered it was good to go.
Got receiver home and left channel still didn't work so I put it in storage for a few months.

A couple weeks ago I figured why not try again so I took it back to Bestbuy.
Rep just gave me call said all was fine with it they re-soldered all speaker connectors for good measure.

I know its not my speakers...Ive tested bad channel on all of my speakers so speaker failure is ruled out.
What the heck should I do?
Bestbuy has no clue what the heck their doing I'm just about over it getting ready to snap on them