I vote flasher too. One side probably has just enough resistance to make the bad flasher blink right.
I had an old Oldsmobile. The right directionals worked fine, the left only worked if you revved the engine a little or, you could just put it in neutral when stopped, and it would work. It was the flasher. For some reason it must have had just a little more resistance in the right side circuit.
Just remember, it isn't the flasher in the fuxe box. That is for the hazards.