Which cleaner/lubricant should I use to restore this vintage door hardware? It is likely 100 years old. E.g. regular machine oil or gun cleaner/oil?
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Graphite has long been a popular lock lubricant. The properties that make it a good choice are that it is dry so it won't attract dust, it can get into very small spaces and it is not affected by cold or heat. It used to be dissolved in alcohol brushed onto the pieces. when the alcohol evaporated it left the graphite in place. Now it is available in aerosols which makes it more convenient to use.
For cleaning it, you appear to have paint on it, so careful scraping with something softer than brass followed by brass cleaning/polishing compound or abrasives for external surfaces. Be very careful about using anything abrasive on a machined working surface. If you want to, brass and copper are particularly easy to polish to a mirror finish. A rotary tool makes it even easier. For the inside parts, I'd experiment a bit with loosening up the crud with a few chemicals before blasting it with a pressure washer if there were parts I had trouble with. A garden hose spray head can achieve significant pressure too if there is no pressure washer available. Cleaning the interior may also be unnecessary and it wouldn't be expensive to experiment with just lubricating it first.