Re: My KM has some rust...
im a fan of mechanical cleaning as apposed to the chemical ways
run some scotch bright pads through it (i wouldnt use steel wool for the fact that any bit that doesnt come out will rust at the smallest bit of moisture and start the rust again)
if you dry it well you shouldnt have to many issues, maybe run some vegi oil/cooking oil what ever down it on a paper towel or a patch like you clean a firearm with just to get a light coating like you would a rifle barrel, that might help prevent rust after your clean it.
a brass/bronze brush from a gun cleaning kit might work well too for the straight parts that are rusted