It might be dirt bunging it up needing cleaning , rather than needing lubricant .
Adding stuff could bung it up even more .
I'd be inclined to try clean it first with something that evaporates easily.
A bit of alcohol might be the first option , or possibly lighter fluid , dribble it down the end then push and pull the end to free it up whilst any dirt is dispersed.
A few applications might flush it out .
If cleaning doesn't work , then possibly try adding a lubricant .
It sounds also that you might have kinked the wire inside it slightly , so when it's curved it gets stuck , but whilst straight it just about manages to move freely.
Can you feel any lumps along it's length ?