This article is from the RCA SelectaVision VideoDisc FAQ, by firstname.lastname@example.org (Tom Howe) with numerous contributions by others.
This condition occurs on the RCA J and K series players when the
function motor belt is nearly worn out. Sometimes the life of the belt
can be extended by using your fingers to push the caddy all the way in
until it latches, but the problem in doing this is that when the
function motor reverses direction to return the empty caddy, the loose
belt may not allow it to eject. Then a small needle nose pliers is
required to grasp the corner of the caddy and pull it out. A better
solution is to replace the function motor drive belt which costs a
dollar and takes about 5 minutes. The replacement belt is PRB No.
SCB3.6, available at most VCR repair shops. If anyone has difficulty
locating this belt you can mail me a dollar (see address in header), and
I'll mail you a belt. I have prepared a CED Player Belt Replacement
Guide that cross references CED timing and drive belts to the available
PRB equivalent, and also provides ordering instructions for all CED
player belts, which can now be done via credit card through the PayPal
service. It is available at the URL listed in question (2.1).