I have issues with the rear left blinker that I haven't been able to correct

You should invest in at least a test light probe if you don't have one already so you can check where power is getting to. If the left brake light also doesn't work then check the emergency flasher switch. Also check to see if the left light works when the switch is activated. If that works then you know the wiring to the light is okay and the trouble is most likely in the dash area. The flasher switch is the best suspect in my opinion.