You might try honing or reaming the seattubes slightly. That should help with burrs and reduce scratching. A solid reamer should help get it round to depth too.
I'm not a big grease fan, but a little lube might help in a few circumstances.
Another thing to try is to sand down a 26.2 seatpost until it fits. If it is painted, then perhaps just taking off the paint. But, you want to reduce by about 0.1mm, or reducing the radius by about 0.05mm... Which isn't very much.
Keep in mind that a lot about the posts clamping react like the circumference of a circle, so a 0.1mm difference in diameter is about a 0.31mm difference in circumference. Not a lot, but it does add up, especially if you're off by a few tenths.