Lisp code can add onto itself. An old computer likely accumulates a lot of errors. However, most of these errors usually come from typos and missing punctuation, so it is a rather low-stakes kind of self-editing Caine is likely used to because he is his code, and he is written in Lisp and this is what Lisp can do.
That's how the olschool pre-AI coding helpers worked, checking your grammar. Maybe he even checks an active and inactive copy, like DNA repair, only because an actively read area likely accumulates more errors.
So he must have a code checker functionality. And maybe some other repair-related features.
A fun angst/whump idea could be digital scurvy, with that exact area of code getting broken down, and Caine not being able to repair himself.
A bone in his rigging got one of its coordinates set to 0;0;0, because the part of the code that traced its position and velocity broke, and he can't repair it, or maybe his levitation (I love me some Caine that can barely walk), or just there's an ID error and some items are now referred to by wrong names. And he either has to figure out how to fix himself, or ask the crew.
