I reduced the inside edge of the receiver gate on my new SBL after I noticed the shaving. I did this by using 1500 wet/dry over a .5 inch dowel. It is not needed to remove metal. You are simply polishing the radius. To do this best you will need to disassemble the rifle. Remove the gate spring also and polish the outside edge while you are at it. Then take the gate spring and bend it, actually over bend it.
While you have the rifle apart, look all the parts over for any burrs. The leading edge of the lifter should be polished. Take a look at the very end points of the bolt, if they are sharp, use a stone to reduce them also. The snail cam on the lever, yah, ever so slightly knock that sharp edge off. Look the lever over good for any other burrs or rough areas.
If you notice a hitch as the round comes up into the bolt face, consider also giving the extractor a slight over bend, gently, and also inspect the extractor for a burr, remove as needed.
I do something like this on every gun I have ever owned, new or used. They have, with the exception of a Kimber, needed some attention.
Mobil 1 grease, just a little bitty bit on wear areas will make the action smooth.
And, just for the record, cycling brass with my rifle does not scratch the brass and rounds load easily like butter smooth. Oh, again, use nothing courser than 1000 and I used 1500. Do a final polish with Crocus.
As to the "Remlin" silliness, my current Marlin is the only Marlin of any era I have owned or used that is actually straight though I have an older 30-30 that is kinda straight if you do not look to close. This Remiln insult is just a way of making people feel badly about their new purchase. Marlin did not need Remington to help them build crappy products, they were pretty good at it before they went TU.
J