It's been my experience that the cable itself is the actual problem.
I disconnected the cable from the tranny, elevated it, then doused the end with oil that I allowed to soak in and to be worked in.
FWIW, I used some of my outboard engine fogging oil. Good penetrating action and is resistant to getting washed out easily. Been a year and a half (almost) and the cable still allows the shifter to move easily.
Steve