The size of the X5 has not been provided - yet. Also, the size of the X6 has not been provided yet but is assumed to be very close to the other X6 variants.
The copper is coated by Manker to give some protection from oxidation but how much protection and what type of coating is not known and the info is not available - yet.
As far as I know, the only way to keep copper from oxidizing is to spray a clear coat on it (vinyl or acrylic or …?). Here is one example:
As for a patina on the copper which I don’t like because that means the pretty copper becomes dull, I would spray a clear coat on the copper ( I have never done this before but this is a plan off the top of my small head):
1) Remove the SS bezel and SS battery tube from the X6 host and put them aside.
2) Use tape and mask off the LED MCPCB at the front of the copper heatsink.
3) Mask the driver PCB at the rear of the copper heatsink.
4) Mask the threads on both ends of the copper heatsink
5) Mask the mating surfaces of the copper heatsink which press up against the bezel and the battery tube.
6) Go to a hardware store and buy a spray can of clear coat (glossy or matte finish) which adheres to bare metal surfaces. Maybe a clear primer of some sort would stick to the bare copper the best? Primers tend to stick best on most surfaces since primers are used to get the final coat to stick.
7) Spray coat both outside and inside the copper heatsink and let dry. I would leave out any final coat - just use the primer.
8) An occasional touch-up job would be required as the coating wears off at various areas.
9) An expensive option is to take the copper heatsink to a plater and have them nickel-plate the whole heatsink. But then the whole host would be a shiny silver.
Also use the same principles above to coat the entire X5 host.
What is the lesson in all of this? Pretty things are high-maintenance items - whether made of copper or whatever - they don’t stay pretty without a lot of work.