put a little oil along the groves, and wait an bit and then put more oil. tapping very lightly after oiling can help sometimes to get them to loosen. just takes patience and oil. Tri-flow is a good penetrating oil for helping to get things to loosen up. Once you get them off, make sure to clean the tracks well.
At least with them being stuck, you still have them. More often they get worn a bit and fit loose, and then when they slide out while the machine is in storage, and get lost.