I haven't heard of any specific product to use for this purpose, and I would soon be in the same situation. I'm revovating some of these windows, removing all paint from the sashes and frames. I think our best bet would be the replacement sashes I saw on the Renovation Guide (I've posted a help message on this to find the manufacturer) I don't want to disrupt the original architecture with full replacement windows, but I do want an upgrade over those old drafty rattling sashes.