For my D1 the problem started after some low life tried to steal the truck.
The Key would needed to be gimmied/wiggled for the tumblers to line up.
Tried graphite, etc. nojoy for over a year then my Indi fixed it right away with a shot of K-57 (i think that's wat's called) and no more problems (I hope I'n not jinxing it now)
For the Canadians, it's available from "Krown Rust Control" but "Home Hardware" carries K-54 that is the old formula but still good.
I'm not having any more problems with any locks and the handle of the tailgate.