Duck oil is water-thin though. I can't imagine it stays around for long. Its very much like the silicon oil I used to fill my' RC Car' dampers up with.
Thinking outside the box here.. are you sure its the bushes and not just a mouse that hopped onboard whilst at the workshop?
I just found duck oil was the only thing sprayed over the bushes that would stop the squeeking for a bit. Obviously the only way to cure it permanently would be to strip down, clean off and re lubricate. It was a stop gap until I could be bothered.
As for the mouse, I have had mice in my old car, I've also fired up a land rover after a few years to have the mouse nest in the radiator cowling be thrown at me as the engine fired. I'll check for that next time I start a car thats been laid up.