Well, we must have gotten lucky, then!
Here is what I discovered. The phone in question, just last week, before the Holiday, was converted from a 5304 to a 5330e. Basically, the customer just changed the phone type.
Somewhere in that process, the form must have gotten messed up, and then the error started showing up in the nightly DBMS audit.
So, my customer changed the phone BACK to a 5304 in the form. Then he cleared the keys. Ran the DBMS Check Full. No Errors.
Set the phone back to 5330e. Put the keys back in. Ran the Check Full again. No errors!
As I said, we got lucky! Here's to having a stress-free weekend! Yay!