Those black drive rings are not very well engineered... it's possible a few of the plastic wheels that center the ring and help hold the two halves are broken.
By all means try CK's idea first, but then you may have to split the halves (they do pop apart - do it gently or you may break some rollers if they're not already bad) and have a look inside.
I believe the newer (gray) drive assemblies are available separately - I remember seeing them on the Sailnet store site... you might try that if you can't fix what you have. Raymarine does not support service for the older rings and you can't get parts. The new ones are much more robust, fewer plastic bits, and more adaptable to varieties in spoke diameter and placement.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"