I use to own an AlAn, 25.0 is right, previous owner may have overtightened the ears
Its a cross frame, so flying remounts may have pushed the post down,
causing the owner to crank down on the bolt, compressing that housing hanger. It's in the slot that is where the seat post clamp squeezes.

I have a run the cable thru the seatpost method I used , so as to not need that cable hanger inserted between the frame seat post clamp.

It's a Campag Super Record single bolt , will sell ..
hand machined roller inside the seat tube,
to make nearly no friction..

If you get a collar machined to go just around the seatpost It would sit on top of the frame.
And stop pushing the seatpost in , if you are going barrier leaping.