Buying a new tube won't work.
The magazine tube is brazed in at the factory and it's a factory-only job to replace it.
This is a hard fact some people learn who fail to use a barrel clamp with a magazine extension.
Bump a magazine extension that doesn't have a clamp, and the extension can be knocked out of line, or completely off the gun.
This damages the threads on the gun's magazine tube, and the gun has to be sent back to the factory.
Remington has to remove everything from the receiver, including the ejector assembly and the shell stops.
The receiver is heated up red hot, until the brazing melts and the damaged tube can be removed.
The receiver braze area has to be cleaned up, the new magazine tube is installed and held in alignment with a special clamp and alignment jig, and the entire thing is put into a temperature-controlled furnace to braze the new magazine tube in place.
Then the ejector assembly and shell stops are replaced, and the entire unit is re-finished.
So, first, do as above and Dremel or drill the dimples out, then smooth the entire area to insure the shells will feed smoothly without hanging up.
Second, USE A BARREL CLAMP, it doesn't matter HOW strong the extension is, it could be a solid steel bar. It's still screwed to the thin magazine tube.