Honda GCV160 Carb Leaking Gas

I have a Craftsman mower with a GCV160 Honda engine that is driving me nuts. Mower model 917-378501 Honda GCV160-AS3A. The carb is leaking gas. I have disassembled and cleaned the carb, washed out the gas tank, put a new fuel hose from shutoff valve to carb, all the gaskets are in correctly. Everything tests fine for a couple days. I return it to the customer it does ok for one cutting and then the carb starts leaking again. I realize the customer could be putting in debris from a bad can etc. It is obviously a needle seat problem of some kind. I need some suggestions on how to remedy this problem -- maybe a filter of some kind -- anything. Are these Honda carbs prone to leaking ??? I don't tend to see the problem with Honda engines on Honda mowers.