Mossberg 500 Slug Barrel Rifling Problems

OK, so here is the deal. I have a Mossberg 500 20GA field/slug combo that I got when I was 13. When I was young, I didn't know that you weren't supposed to use rifled slugs in the rifled barrel. Over a period of time (and a successful deer hunt), quite a bit of lead fouling built up and it started to turn into a smooth bore (however the damage is not from the type of slug).

Well when I finally realized what was going on, I cleaned it very well and I was able to remove all of the lead fouling. However, I discovered what you can see in the picture. There is what appears to be rough machining marks on the lands of the rifling. The red outline is around what I am talking about, and the blue is around how it should look. I can feel the machining marks with my fingernail when I run it over the rough spot. The edge of the lands are sharply defined as they should be.

I haven't really noticed any accuracy problems (shots touch at 40 yards with irons, but that might have been luck). Is it worth going though a warranty replacement with this, or should I just ignore it and keep shooting?

Any opinions here?

Ok, well I will go with what you guys are recommending! I thought that this was uncommon, but I guess not. And about cleaning the fouling......... never again will it get that bad haha. The funny part too was that I had been using high velocity sluggers, which grouped about 2ft at 50 yards. I was new to shooting and I thought I was just nervous. Now thinking back it was a miracle that I hit my first deer (it was a clean kill, dropped instantly).

Thanks