I've been rustproofing cars for over 20 years. I made a hobby out of it. I even picked the brains of corrosion engineers when I was working at Chrysler. There are a few facts I can state:

- Washing alone will not keep a car from rusting. It just helps by removing the dirt that can cause poultice corrosion.

- There are no "lifetime" rustproofing treatments.

- Even a rustproofed car can rust out, unless you can guarantee 100% coverage that won't wash off.

That said, I've been rustproofing my cars for over 20 years with a compound called Texaco Rustproofing Compound. Like jjl, I converted my paint sprayer to spray rustproofing compound. The compound needs to be reapplied every few years, especially in the high wash areas. But I've never had rust on the protected parts. The only rust I've had is where it originated from the outside or in the A- or B-pillars, which are closed sections.

I tried oil. Didn't like it. It disappeared, never lasting the winter and left the metal dry.

I've had mechanics praise my work during buyer inspection. Nothing like rustproofing a car yourself for a job done well.

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95 E320 Cabriolet, 169K