More likely to be the cables getting stiff than the controls. I've replaced cables on ours and the controls themselves have never needed anything doing to them - there was plenty of grease on the bearing surfaces inside when I stripped them down.
Edit: it might be worth changing the cables anyway - our new ones were much smoother than the old ones, and the only reason I had to replace was that one of the old ones snapped...
I had trouble with mine. I disconnected them, taped a small funnel over the end and then sprayed RP7 or similar into the funnel, let it work in over night and then pushed and pulled the middle of the cable so that it worked the lubricant through. That was years ago and still going strong... touch wood.