Send it to me and I will dispose of it properly. Just kidding. The previous owner must have installed an undersized post and then clamped the frame down tight. You will find it very difficult to fix. My experience with that problem on a Homegrown frame (6061): my LBS had a nice reamer/cleaner tool that cleaned up my seat tube to a shiny new finish. Removed the seat clamp. Tried the proper 26.8mm post with no success.
Here is the trick……Todd (my hero) installed an old quill stem into the seat tube. He tightened the stem bolt which expanded the seat tube. He did this a few times in a few different positions inside the tube. Warning!!!!! DO NOT OVER-TIGHTEN…. Your not trying to make it fit a 27.2, just a 26.8.
Good luck.