Is Fiberboard sheathing under cedar siding ok with no vapor barrier?
To me, moisture barrier goes on the exterior side of exterior walls and vapor barrier goes on the interior side.
We install moisture barriers because we know siding leaks...especially your type of horizontal lapped siding.
If you are patching a hole (or small area) in the siding, there’s no reason to remove all the siding to install a uniform moisture barrier throughout the wall. I’d just make sure the patched area has an adequate moisture barrier and it’s lapped properly onto the existing moisture barrier before installing the new patched-in siding.