I am not near my pictures so you will have read some text.
Make up a copper insert that will allow you to weld up the wear point.
I used a dremel fiber cut off wheel to make a seam line.
While not critical, i also made a round 'anvil' that fits inside the tube. This allows me to hammer the tube to correct the shrinkage.
The original hole on the top was just the edge of the formed sheet metal. I was at an angle like the taper you put in for countersinking a screw. Most tubes are completely worn into a MUCH larger hole. I put a copper rod inside the tube, fit does not have to be perfect. The copper is just to keep the weld thickness thin. Then weld up the top. Drill the proper ID hole with a regular drill and then use a countersink drill to give the proper taper.
I also weld up the pivot hole at the base and redrill the usually well worn hole. I made a simple jig from a 1/2" pipe fitting to let me get the new holes in the right spots.
Check the magazine indexes. I believe there was an article on rebuilding them in the last few years