speedometer cable?

[Roper]

I just got a new speedometer cable for my 81. Now I always thought that when you get a new cable that you have to pull the inside metal part out of the black plastic sheath in order to lubricate it.
Well on this new geniune GM parts speedo cable, well I couldnt pull it out by hand. Like you can move it in and out a half inch or so but thats it. I even took vise grips and tried to pull it out. Well I didnt try as hard as I could have because I didnt want to screw up the new cable<that cost $80>.
Also on this cable if you look at the ends there is already grease on them. The cable <what I can see> looks like its already lubricated.
What are your thoughts? Should I take vise grips and really come on to it to get it a part to lubricate. See the one end is serated/groved metal and the other end looks plastic. I dont want to screw up the ends.
Or is this a type that comes pre lubed and isnt meant to come a part?
The mechanic at the GM dealership thought that it should just pull out to be lubed. However between you and me those mechanics in town dont seem to know much about anything that isnt a computer.
Any oppinions?