Is this the cap you have?http://shop.lenovo.com/us/en/itemdetail ... EF35E17525
If so, it looks like the older caps may not be compatible with it, due to the different-sized hole at the bottom. I haven't used any of the new Lenovos, but the comments are shocking. It looks like while we were busy ranting about the ruined keyboard layout, Lenovo actually went on to ruin the trackpoint.
I have a Compaq Evo N610c, which had come with low-profile caps, and the difference in usability between that and a standard old-style Thinkpad cap is night and day. Fortunately, that Evo could take a standard Thinkpad cap, but the new Thinkpads apparently cannot.
If yours looks like this, there may be hope:http://shop.lenovo.com/us/en/itemdetail ... EF35E17525