now too late liao.
i dismantled the set, shone torchlight thru some of the openings and found a lot of rust inside, mostly at the bottom and at near 1 of the front ports (links to the regulator)
when i removed the rear safety valve, even the threads itself has some rust and on the outside of the tank near the threads.
i think, no point for me to remedy the situation. I was scrubbing the insides with a sharp metal wire to scrap away the rust then clean and dry it. after that, pour some primer inside to coat a layer of primer.
but after cleaning, i realised too much rust for me to clean. just going to use the airbrush until it spoils loh. unless I can get some acid to properly dissolve the rust away.