hi
got about 10 of them in my shed all exactly the same ,, all drive chains have got a tight spot in them and my thoughts are that people have tightened the drive chain too much and when they have rode them over the years it has slowly pulled that tube in . its not that hard to replace and make it out of thicker wall tube , hydraulic tube if perfect . if you look at the same section on a B29 they never bend . hope this helps .
yours carl.