I've used Rust Bullet on a very small area that started due to a plugged trunk drain. Got to both sides of that one so I'm golden. Also used it underneath my battery tray and on the tray itself, and on some surface rust in the engine compartment sunroof drains(which were plugged up too). The car was taken care of, just the drains were ignored since not everybody has the inside scoop on this stuff. The Rust Bullet is good to use for tight hidden areas, you only have to knock the loose rust off and paint a couple of coats on it and you're done.
I recently bought some jack hole plugs. My jack points are rust free, and what I did was pressure wash them out, roll up one of those blue paper towels, run it up into the holes to get the excess dirt/water out, roll up another one(I'm good at rolling things
)slather some wheel bearing grease on that one and run it up in there, just to put a light coating inside, put some grease on the end of the plugs and plug 'em. I'll never use those jack points most likely.
Regarding the Fluid Film Spray; I understand that it's good to spray it inside the rockers. What do I remove to access the inside of the rockers? I see there is a cover of some sort at the rear of the front wheel wells- how does this come off? Someone do post a list of the likely places on w123s that could benefit from a liberal application of Fluid Film Spray.