Small spots like that can be taken off with MAAS and a Q-Tip. Its usually because moisture has got at the blade, making it tarnish slightly like that.

What you're doing now sounds fine to me, but something you can also try is to put a couple of packs of silica gel in with your razors. This stuff takes the moisture out of the air and works really well at preventing rust or tarnish.

Good luck and keep us posted!