It's possibly where the grease zerk sits in the outer tube. I have seen that on mine in the past.
Not much you can do to clean it up that far into the tube. I usually just clean up the shaft and grease them up good.
Grease zerk or a little weld bubble rubbing. If its a threaded zerk, remove it, file a little off the end or shim it with a washer if it protruding inside. Grease the entire shaft when you reinstall, don't rely on the zerk getting the grease end to end.
I’m thinking some of the welds burned through as well as the zerk. Maybe remove grease zerk, wrap a long drill bit in sandpaper and kinda smooth\ hone it out.
By the looks of the thickness of the welded bung that the zerk threads into I don't think the threaded end would reach the aluminum shaft. More than likely a bump of weld that burnt through to the inside.
Assuming it's not bent and just a little welding slag / filings from zerk ...take a long dowel or piece of pipe of smaller diameter with a bit of sandpaper and dress it up .. if It's bent then a little persuasion in a press might resolve it