My point is that one does not know what problems there may be without overhaul. Once overhauled a classic Sturmey can provide reliable operation for years, even beyond a decade. I am well aware of the use of oil in Sturmey hubs, having overhauled perhaps a hundred or so. It's still nice to have grease in the outer bearings. As for flushing it out, the labyrinth seals at the outer bearings make effective flushing rather difficult. The OP would have likely spent less time with a simple overhaul than what he will have put in trying to avoid it, and he has no assurance that something else is amiss inside - rusted springs, larger debris from poorly meshing parts, etc.