I haven't tested this, but this might work for making the sharpie more permanent.I painted my silver battle rifle with a sharpie and it came out pretty good. However, sharpie will not stick well and can be scratched off with ease.
Wash the parts in soap and water, once dry sand them with a high grit paper to remove some of the protective coating.
Very important to use a sand paper that isn't too rough or you will see scratches when you sharpie it.
Once sanded, sharpie the parts and spray clear a finishing or you could even use clear nail polish.