• When we replaced the BB we were also retapping the bottle cage mounts and a lot of WD40 went through the downtube. All came out very orange and rusty... Certainly nothing feels to the extent of major/flaky rust though. It has been inside for the whole time I've owned it, I imagine that atmospheric moisture is enough to cause a thin coating of rust on the inner surface over 40 years (or thereabouts).

  • A coating of oil of some kind will probably go a long way - but it will also need time to cure/harden, which means leaving the bike completely disassembled for a while.
    I wouldn't bother, unless you planning on a major strip down of the frame anyway.

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