I can't say as I've ever lubricated anything in the shifter extension. For one thing, it seems to get enough (if not too much) "stray" lubricant from other places (presumably the gearbox itself), and for another thing, it's all pretty much nylon bushings that really shouldn't need lubrication.
I'll be interested to hear other opinions on this. Meanwhile, I don't think I've ever heard of the specific problem you had to address. I've rebushed more than a few of these shifters over the years but never had to replace any "hard" parts -- just bushes!