Agreed. Something like Saphir's Renomat should do the trick in removing build-ups. Maybe some Lexol to soften the leather after all this dry polish, and my secret cream is Crema Alpina. It has proved more effective than anything else I've tried over the years.
emiristol, I posed the very same question some months ago on this thread when I found out about the topic. Back then, SF member VegTan answered that, yes, historically they have been untouchables, but this distinction does not hold in modern Japan.