How can I fix the switch on my Cuisinart DLC-8 Plus?

My beloved DLC-8 Plus has been having trouble locking/running for a few months now, with the slide/lock mechanism at the rear of the work bowl failing: The once sure 'click' that told me the bowl was in place/ready to run has failed completely, and now won't engage at all.
I've removed the bowl, and found a small black rubber indentation that looks like a depressed button. Having never questioned how it worked before, I don't know if it should be up or not, but something is definitely missing as the bowl no longer engages when slid clockwise, as if whatever once 'caught it' is no longer present. It also rests beneath a spring-loaded tube, which I assume is part of the locking/engagement process. Any thoughts would be appreciated. Thank you in advance.