If you can trust yourself to be careful, you can get a few tools and "re-point" the checkering yourself. That will sharpen it up and can take a few years off the appearance of the rifle.
If you don't care to learn, have it done. Then before any oil is applied, you can brush it lightly with a walnut stain that will darken it. Apply this sparingly and carefully so it doesn't soak back under the finish adjacent to the checkering pattern.
When that has had a chance to set up, (overnight is usually good) re-seal it with oil and you're good to go.
I start with a couple light/medium coats of tung oil applied with a toothbrush so it can't pool in the grooves. When that is absorbed (dry) I topcoat it again with a couple coats of Tru-Oil cut 1:1 with lighter fluid (naptha mostly). Again with a toothbrush.
This type of detail work can really improve the looks of the rifle and add value as well.