Are your Collaros the early models? Gold,or silver baseplate,black tone arm/overarm,9 inch turntable? Model # under the turntable mat,something like K-600 or G-600? If so, those were lubricated with an early type of lubricant that would get gummy as it aged. Those changers need to be torn down,cleaned and relubed. The later models usually just need the drive wheels and pulley cleaned with alcohol,and adjusted.
If you cannot do the repairs yourself,I can overhaul them for you. I do have a some stock of Collaro parts also. You would have to remove the changers from the cabinets,to do the repairs,other than drivewheel service. Do you know how the changers are removed from the cabinet?