Wow, perfect timing. I actually JUST addressed this on my dad's LX this past weekend and was planning to update this thread. I'll walk you through my process.
I did reach out to Ospho and sent them some photos and a description of what I was looking for, and they actually did not recommend their product for this application. Their response was, "You can try to clean the stains but to address the rust, it would need to be sanded, treated, primed, and painted. Ospho is a rust treatment. Will not work without sealing it."
I was not planning on sealing anything, so I chose Fluid Film instead. I assume I'll have to do this once every season or two.
I used WD-40 and a rag to remove the existing rust stains. I found liberal amounts of WD-40 were needed, and it worked best if I sprayed it directly on the rusted area (instead of onto the rag) and then I left it alone to soak for a few minutes. Then a little more WD, followed with some elbow grease got ALL of the rust stains off the underside of the door, the rocker panel, and the lower tailgate weepholes. Per
@roadsalt's post above, the clips inside the cladding are still there and presumably are still rusty, so after cleaning up what was visible I sprayed liberal amounts of Fluid Film inside the doors. Using the included straw, the FF could be sprayed throuh the weepholes in the bottom of the door. I sprayed a lot, stopping only when it started leaking out of weepholes. Of course I didn't take any followup photos, but I can request some from my dad if that would be helpful.
