What confuses me is that (with the bad speaker gone) it’s now the left-rear only, and not the entire left side.
I’ve never heard of that.
you might well have 2 bad speakers now......put 2 good speakers with the same resistance as the originals on the left side......if it works it works....if it STILL fails shortly after firing it up, buy another stereo or amp or whatever the output is.....one last time, traver the wires for short to ground..........prob is centered around more current than the output can stand......find it or get out your wallet:)