I am trying to treat some of the rust on my 220D. For internal cavities where access will not be possible after the rust repair, which is a better treatment:
1) a zinc phosphate coating like this:
Internal Frame Coating w/Spray Nozzle | Eastwood
or
2) a yellow cavity wax type coating like this:
Heavy-Duty Anti-Rust in Amber - Rust Proofing Products - Eastwood

I am not committed to Eastwood necessarily, as many others make similar products. But am just trying to figure out the best approach to preventing further rust on internal cavities. I have seen both types of products recommended here in DD, so am a bit confused how to proceed. Thanks.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).