last night i got month 24, that has the parts for the head motor and shaft.
in my package the mounting shaft had a bit of some rock like stuff stuck inside.
if you do not see it and try to assemble then it will not fit right.
so check the part.

i have two photos to show the part and where the rock was.

no need to do that in my case.

i got the rock out of the shaft and the center axle rod fits in the way it should.

if i had not been able to remove it then i would need a replacement.

by the way it was a chunk of "polishing stone" used to finish a part.
generally not going to get one stuck inside like that but i can happen.