Thanks for the suggestion. I hadn't heard of Noxudol, but seems legit from a few minutes of searching. This post on this GarageJournal thread (along with a 2014 thread started by the same person) make a pretty good case for it. Partly due to anti-corrosive ingredients, and partly due to its waxy consistency which helps prevent it from getting washed off. He's not a big fan of FluidFilm, but the first link has a lot of testimonials from happy campers. So to quote the great Roy Underhill, "Yes it works in practice, but does it work in theory?"If it's gooey/waxy it might be a Fluid Film type application. If you don't want to deal with it, APS Rust and Tint in Fairfax could look at it and give you an estimate. They clean the undercarriage and treat with Noxudol's line of products. I had them do just the cavity wax on mine, which seems similar to Fluid Film. I just had it done but have gone through undercarriage carwashes a few times and it seems to be holding up. If you do just cavity wax, expect to redo it every year or two.