Good day everyone !

I just bought the very first to me AR-15 rifle, a Sport 2, and took it to the range for the first time yesterday, firing a hundred of Federal FMJ rounds with not one hickup . Only shot AKs before and never cared much for their ergo. The AR is a pure joy to shoot, by comparison (not sure how much is due to a lighter round with less recoil, but I think ergonomical design has had a lot to contribute there).

Two questions that I hope you may help with:

1) It has a fixed A2 style front post and a flip rear sight with a peep hole. At 50 yards I could barely see the 2" bullseye (the diffraction caused by the peep hole didn't help my eyes to focus either). At 100 yards I'm lucky to see the target. I want to put a sight on it to make shooting more enjoyable, while keeping the iron sights for backup. Asking questions here and there, it seems there's really no good way to mount a traditional scope on this gun without removing the front post or sacrificing the ergonomics - is this correct ?

Would going to a co-witness red dot (I was eyeing Bushnell TRS-25) and a flip-out magnifier help ? Any other suggestions ? I'd like to keep it under $200 total.

2) I ordered it from an online store, and while inspecting at my FFL saw what looked like a line of baked - on grease on the receiver starting just above the bolt catch and all the way towards the barrel. The area back from the bolt catch is clear & clean, and this is the only imperfection on the rifle. Upon cleaning and further inspection, I now think it's scuffing. Most likely from the factory.

I don't want to send the rifle back to S&W to fix a cosmetic damage - it would probably take weeks and cost me $50 - and was thinking of getting Aluminum Black pen and just covering the marks up. Any reasons why this would be a bad idea ? Can I use AB over already anodized aluminum, or does it only work on clear alum ?

TIA !