Bit late to check the lathe now but after googling what a tenon and camp screw is I will be sure to check them. A visual inspection shows nothing wrong with the keyway. All I did in reassembling was cover everything in oil.
I don't usually remove the centre. Only did it then cause it might have been causing the jamn. Your use of the little hole does make sense though, that might be well the official way to do it.
Speaking of centres can the tailstock take a MT 0 taper? I read somewhere that it is a non standard size but now I can't think where I saw that.