You could check the wiring from the A frame into door in harness for damage and pull doo trim if needed and check / lubricate lock linkage , lock assembly

 

I’ll make sure to check wiring. Is the inverse key direction to drivers-side normal?

 

Check for a bent snipper rod inside the door or a misaligned or broken surround around the button.

 

If the rod is broken. Are there direct replacement parts? The passenger door still unlocks and locks fine with the key. Could still be an electrical issue.

 

They usually just bend rather than break. The plastic rod retaining clip can go missing or break nut they are fairly generic an readily available e.g. Pardon our interruption...and They usually just bend rather than break. The plastic retaining clips sometimes break or go missing but they fairly generic and are readily available e.g. Pardon our interruption... and Pardon our interruption...

 

Ok. I’ll have a look into it when I get the opportunity. Your initial links were for an early Australian Fairlane’s, still same/similar parts?

 

Not the first time in the " dark ages " that I went into my bodyshop and nicked a welding rod to use for linkage . Another favourite to use was a wire coat hanger which also was very handy as a car aerial / antenna as a temp measure if it got snapped off