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Sorry I missed that you had problems with the levels in the clamping plate of the head, and I obviously assumed it was the tripod that needed a new level.
As far as I know, the model number you gave leads only to the legs of the Gitzo tripod, and does not specifiy the ball head. That is what had me jump to thinking you needed to fix your tripod. There are a wide variety of possible ball heads you may be dealing with, and you should try to determine the brand and model you have. Once you do that, you can inquire about replacing the quick release clamp with a new one, and get that inquiry to which ever company made the head. If you now have or want to change to an Arca Swiss compatable system for your clamp and plates, that would bring me back to recomending Really Right Stuff, and getting a screw knob or lever release clamp that has an integrated level built in. The levels in RSS clamps are a round single bubble level that gages both directions in one level vial, so they are not quite the same to use as dual level vials, buit still work well. If a RRS clamp is of interest to you, they can help you choose a clamp that will go on your ball head, assuming you can determine the brand and model you have. Actual Gitzo ball heads are not that common, but that may be what you have. And if you do actually have a Gitzo head, it may not be practical to adapt a RRS clamp to it, but you would then be back to looking up the Gitzo head model on the Gitzo spares web site.