How do you fix adjustable awning poles ?

G`day,
I went camping last week and when I attempted to erect the awning some of the adjustable poles would not lock.
The type of pole is the two piece aluminum ones with a nylon "cam lock" on the end of the inner piece that locks against the inner wall of the larger tube when the two pieces are twisted.
I bought these poles a few years back because they are very light weight and they also bundle together neatly as there are no protrusions to catch on others when removing them from the pole carrier tube on the van.
They were ok last time I used them, twelve months ago, and now they won`t grip.
Does anyone know how to fix them or if the "cam lock" piece is replaceable, if so from where.

Thanks

Scrubby