Heat exchanger flaps

I’m about to replace my heater cables and I’ve noticed that the left side heat exchanger air flap isn’t spring loaded to shut where the right side is.
Presumably, this spring loading is needed to pull the cable back as the lever is raised at the front?
Is there any way of repairing the heat exchanger or could I fit an external spring to the mechanism?

 

Post a pic of your spring-less one.

 

It’s there to close off the heat with the secondary effect of pulling the cable

 

You may find that the one with the spring is the broken one..as the spring is not standard fit.