Thanks for the feedback. Still want to hear from anyone who has used the RPM. Will look into the T-9 products.
I have a jug of Ospho and another similar product called Rust Mort. I use them as paint prep on rusted metal. This reminds me that I need to wipe down the roof on one of my Rancheros! I haven't been able to get a consistent finish with Ospho, so I haven't tried it on parts that don't get painted. The streaks on the hood are typical of my results....not really what I want on a part that's supposed to be bare. This RPM stuff seems like it would be good for hood hinges, master cylinders, suspension parts that are typically left bare, etc.
Since posting this, I've done some more research and found a couple of guys who have done tests on multiple products....none included RPM, but interesting none the less. Beware...one of the guys was showing that plain WD-40 and product called Fluid Film were performing remarkably well. At the 1 year mark, he realized the sample metal was tin coated, where the rest were bare. I contacted him and he still believes the Fluid Film is a good product....just be aware, results on WD and FF are meaningless. I guess he's doing a second test that's in progress.