I wouldn't worry about the black lines on the pins. I don't think they affect anything.
Just use baking soda. The rhodium is fragile. For that matter so is silver plate, which is the layer underneath the rhodium. I know, because my brass now is starting to peek thru in spots, because i got too overzealous w cleaning. Fat Daddy Vapes carries rice pins. Because other mods, like your Roller, and the Nemy use them.
I would maybe not use chloroform to clean your contacts. Fumes are toxic.
Hey, ya know what? After endlessly cleaning the snot out of my Poldiac switch, and still having problems I finally got it, and I feel like a total idiot now. When I'd set it down the battery would bounce on the spring in the bottom. It shouldn't do that. It was hitting weak again today, and with a freshly charged battery in it. So I screwed my voltage checker into it, and got flashing 8's. A bit of thought on this and I arrived at the conclusion that it wasn't the switch, which I'd cleaned obsessively, but it had to be the spring in the bottom of the mech going weak. I'd noticed the battery bouncing inside a couple times, so that had to be it.
I pulled out my little plastic bag of springs from MMV, put a new one in there, and wonder of wonders, it suddenly hit like brand new! That spring is out of sight and out of mind most of the time and I never gave it much thought until now, but over time they do go weak on you, and that's going to hurt your contact current making your mech hit weak. I'd prolly have picked up on this earlier if I weren't so crispy around the edges from 18-22 hour shifts all the time.