American Standard Faucet Repair

I have struggled with American Standard Faucets that are 1956 vintage for 20 years. These are the old style with a boot over an articulating rounded pyramid at the end of the valve.
I have completely rebuilt them many times (new valve seat, rubber gaskets and complte valve units).
However, there is trouble with water flow. It is quite limited.
I have tried to correct this by backing out the outer sleve. That sort of works but the faucent tends can leak and the user can actully start backing the sleve out of the fauct.
I have wondered if the problem is that the new valve seats are higher than the old ones were. However I see no lower valve seats at the store.
Does anyone have a solution for this?
Thank you,

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