Deltadart,
If that sight can be disassembled, all the better for your BC plum brown application process. I think you'll like the results, just follow the directions on the bottle; very easy to do, and very quickly done. Just make sure to completely degrease before you start, and make sure to rinse completely after the process to stop the oxidation. Put the oil to it (your preferred gun oil will work; I like WD 40 for a job as this one), wipe it off, and you're done.
Rubber gloves, a face mask (should be handy these days, eh?) and good ventilation is your work area requirement. I'd use a clean, 100% cotton flannel patch for an application like this one, and a hand held propane torch for heat; doesn't take much heat to make the "sizzle" on a small part like your sight.
Good luck! I think you'll like the color.