As mentioned in the other thread about blinkers, the Flasher module operates both the left and right turn signals, so is likely not the culprit. Here'* another fairly recent thread that addresses the same (but right side) issue:
From this, I recommend:
- Check the bulbs in the left side for corrosion, bad contact, or bad filiment (going bad).
- Check the bulb sockets for corrosion
- Check the lamp wiring connections for looseness, partial breaks, intermittent shorts.
Those are my bets.
Oh yeah, the link:
Blinker fluid Link