It would depend on what Harris regulator you have. The smaller cheaper ones can be boughten new for about what it costs to rebuild them.
I sent mine to:
Jerry's Welding Supply Inc
5367 US Highway 50
Hillsboro, OH 45133-7532 Phone: (937) 364-1500
Asked for Bob. He is super fellow to deal with.
They have someone that rebuilds them for them. My local Gas/welding supplier out here in Iowa told me that the older Smiths that bolt together could no longer be rebuilt. Set them to Jerry's and they had zero problem. It cost me about $65 including freight.