Those lines down the casing is from the fluting in the chamber, 100% normal.
These are notoriously hard on brass.
It is very easy to damage/bend the extractor spring if you do not use the correct method to remove and replace. Use a pick or other tool to rotate along the axis the spring pawl from the dish of the extractor, DO NOT PRY IT. Once rotated it will slide forward and clear of the bolt head, then lift your extractor off, clean and check for wear and damage. Reverse the process to replace with a new spring. Always recommended to buy a spare spring since it is a wear item on these.
If you have +6 in there now that poor rifle has been milked and prodded along long enough. Its time for repressing.
--Normal / Normal / Normal
--Loose extractor = needs new spring = will cause extraction issues
--Roller-locks are meant to be run relatively dry. Dry lubricant on the recoil rod (we use remoil). Weapons grease/FireClean on the bolt carrier rail channel and on the receiver rails. Same on the shoulders of the LP. That's really about it.
-- +6 rollers and your gap is 0.0025" yeah, the gun has been shot a ton and/or poorly maintained. Might even need to new barrel.
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If the is Hk91 or G3 style...bolt gap spec by HK and for all others is .008mm to .020mm with .014 to .016mm being excellent. But the person above stating barrel replacement or repress to correct the lack of gap, is 100% correct and this low a bolt gap reading is indicative of a well worn rifle.