I did repair a hole in a copper cylinder once, I used a VERY large soldering iron and puddled solder over the hole, it never leaked again.
For a split you would need a close fitting copper pach, clean the area very well and preferably 'tin' the cylinder and patch before trying to solder it on. Again, your going to need a VERY large soldering iron because the copper cylinder will rob the heat away from where your working.
Martin
December 2007