If it is the valve that I think it is, there is no rebuild, time to replace.
There are a few types, box stores, on line and there might be a dealer in your area that is not of the name brand..
There is the all in one , the media tank in the brine tank, most likely like the one that you have then there are the ones that have the media tank and then the brine tank as two parts.
You might even be able to reuse the brine tank and the media tank with new media and a new valve with meter and a new brine float assembly and keep the brine tank where it is.
The water lines might need some rework but you should be able to save some of the parts that you have right now.
Depending on skill level and if you wish to start fresh or rebuild ...
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