Rega Planar 25 problem

My Rega Planar 25 has an obvious problem: the small round black plastic piece that fits over the motor spindle (i.e. the little shiny steel rod. about 1/8" diameter, that turns with the motor)is not fastened to the motor spindle: it can be lifted off with no effort, so it isn't a friction fit, and it shows no sign of glue or cement or the like.

Does anyone know how these two pieces are supposed to be held together? I have a Rega Planar 3 too, and what look like identical parts (except with no shiny steelin sight) are firmly held together. It's a mystery why my 25 ever worked, but however that may be, it sure doesn't now!

Can anyone help? I posted a similar message some months ago and was told to contact the USA Rega distributor, which I tried to do. No answer came back.

Thanks,

Tom Patton