If you can remove the cable from the sheathing then lube is fairly easy
What I did with mine was to extend the cable all the way out at the motor end and apply a liberal
coating of 90 weight gear oil. Then I attached the end to the rafters and let gravity do it's thing.
Also kept working the controls back and forth.
Did this everyday for a while and now they work good.
Can I say for sure that it was the lube that did it. NO. But I am sure that it helped.
Good luck.
Lets hear what anyone else has done.
Torchie.