If you access an adjustable reamer ,
(maybe the reaming pinched spots will help, <blind Guess>)

I used 1 and took it out 0.2mm ID..
say, get a 26.8 post , a more common size it seems..

then you shave the ID to Just fit , the post you have on hand ..


IDK your bike situation 1st hand , so I'll just relay my project.. BS RB1 27.0, is now 27.2 .

like JDT says , angle the ST opening downward so cutting oil and chips fall out .

it was more wipe down the reamer and re oil, and shave a bit more..

I never made more than a few thousandths of a cut at any 1 pass because I wanted a clean Fit.

when done, very little clamping force is needed.