Leakage around the accelerator pump shaft is a function of the fuel level being too high in the bowl; not a failure of the accelerator pump.
Often, when modern fuel evaporates, it leaves a gummy residue. This can cause the float to stick and the fuel level to be too high in the bowl when the engine is started after prolonged non-running.
Generally, filling the fuel bowl through the bowl vent, and allowing the carb to sit a few minutes, will allow the fresh fuel to dissolve most of the glue.
The solution: start the vehicle more often.
Chances are the situation has corrected itself by now. Try it.
And to answer your other question, leather is far superior to any current synthetic for accelerator pump material.
Jon.
