In this pic, the rough grinding is about half done. After all of the roughing out is done, you start removing metal with a file. This takes forever!!
Here is the finished product. I bored the new tube out to barely slide over the top of this one.
Here you can see the bored out hole in the new tube, and the holes that have been drilled in it for plug welding. This will be a super strong fix and last thousands of miles.
Here is the seat post placed over the top of original sleeve and ready to be welded. The only way that you will be able to tell that this repair was done, will be the difference in pittting. The frame has a little bit of pitting, and the new seat post has none. Once it is painted, the repair will be un detectable.