Job done!
Pulled out the lock cylinder and cleaned it thoroughly with WD40.
Then blowed it with pressure air and lubed it with Silicon WD40.
My advice: While you’re there, do the same with the actuator. Mine was almost jammed by old grease in its “tunnel”, was hard to slide in.
In my case, cleaning the lock cylinder only was half the required fix.
Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.