I just looked at the two old 4506 slide stops in my spare parts kit and neither of mine have any wear on the inside of the nub that catches the slide like yours has. I'm not saying they don't have as much wear as yours has - I'm saying neither has ANY wear on that spot.

I don't think this is going to take much deduction on this issue - change the slide stop and the sideplate assembly and you should be good to go. When you are buying the new pieces, just be sure that they are for a 4506 and not a 4506-1, -2 or -3 just in case there were other minor changes that I am not smart enough to know about.