My wife has an X23 series model 2662 IBM ThinkPad. For years, she's avoided using the TrackPoint pointing device embedded in the keyboard as the standard rounded one was extremely abrasive and worn. She'd always attach an external mouse or (after meeting me) a trackball, or when in need using a piece of tissue to protect her finger. Well, dutiful husband that I am, I finally bothered to do a Google search if there was some replacement nipple or eraser tip for her model.
I was happy to find that Lenovo sells an inexpensive ThinkPlus TrackPoint Cap Collection. So for $10 shipped, I bought a variety of replacement caps, and she likes the wide flat type with the rim. Much more comfortable.