I agree with the comment about waiting for a bit. Since the area you used the Magic Eraser on is darker than the rest, it probably just needs time to allow the stain to evaporate. If you had sanded down to a rougher finish, it wouldn't be darker. I just totally sanded my countertops down (over-polished somewhere along the production process), and they were much lighter gray when I finished. I would say though that if you are already worried about trying to remove oil marks, you are going to be pulling your hair out trying to keep up with it, particularly with a lighter color of soapstone. The whole point of soapstone is not worrying about those spots, which is why I think most folks end up oiling or waxing.

OK...let's see what happened. Magic Eraser is SAND PAPER (it is EXTREMELY HIGH GRIT artificial sand paper). What you did was scrape off the finished surface (and yes...many concretes have colour in them). You exposed some of the aggregate underneath the surface (sand, stone, pebbles, etc). Concrete is POROUS....it LOVES to grab ANY liquid you offer it. It loves to absorb water and oil and soap and grease and suntan lotion, hand lotion, skin oils, salad oil, etc. Concrete loves to STAIN. It is porous (see above). Anything that gives it 'colour' (ketchup, mustard, saffron, etc) will make concrete happy. At this point, I recommend you leave it alone. Give it a month. If you can still find the spot you tried to rub out, I would be quite surprised. Your concrete will change daily. It will stain. It will absorb. It will fade (UV exposure). It will degrade (spalling = crumbling) a little bit each day. Concrete is a utilitarian surface. It is meant to be hard and tough. It is meant to take abuse. It will do this while changing every single day. Relax and let it happen. If you don't it will drive you crazy trying to correct it.

A magic eraser is a melamine sponge, which is basically a mild abrasive. My guess is that your paint wasn't fully cured, so it was more susceptible to "sanding" with the magic eraser. I'm not sure magic eraser is recommend use on any painted surfaces, but newly painted surfaces are most easily damaged. I'm not sure what you mean by chalky marks, but if you've changed the sheen, you'll need to touch up the paint to get it back. I can't speak to super paint vs. emerald, as I haven't used either: I prefer Benjamin Moore paint, and have had issues with Sherwin Williams in the past (exterior and furniture). You might try going to your local Sherwin Williams and talking to them about the pros and cons of the two lines.

You could try a headlight restoration kit before purchasing a new door, I suppose.