[morzh]

Tried to install everything back.
The idler's bushing is a bit taller than the original one and so there's less space on the axis left for the fixing hub with the set screws.
Hopefully it is still enough to grip.

I have just found out why it is that one screw was loose and the other overtightened: the loose s rew is not in tact a set screw, or at least not an original type; it has a non-threaded head and the threaded part length is shorter than the hub's thickness, so it simply doesn't go through and grab onto the axis.

   


So they overtightened the remaining screw. Which is now a bit mangled, so I will have to get a new pair of M3 set screws.