I suspected that the pads might have lifted off. That's what the moisture does, lifts the copper laminate off of the fiberglass. Cool thing is that the circuit can still work just fine even if it is lifted up a bit, but since SMT caps are top-heavy they can eventually fall off.
I second what John said, just follow the traces and tack a cap on there. Easier to use one with wire leads than surface-mount for this. If it works you can always use a cyanoacrylate adhesive to keep other large components from moving around. I know it seems disheartening, but these old PCBs can endure a lot and still tick on.