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plenty of things to try
If you want to remove rust chemically, you'll end up at oxalic acid because none of the others actually works. It's readily available in small pack for a few quid, but be careful because it's not tame like citric and acetic acids.
For mechanical removal with minimum threat to the engraving, lap it on the flattest surface you have. You can use 3M™ Spraymount™ or similar to stick a sheet of abrasive paper to your flat surface if the surface proves a bit slippery. WD40® works as a cutting lubricant
gbj_tester
Cheers for all the various cleaning suggestions, plenty of things to try there. Will probably start off with the things that I've got handy and then build up.