common and variable widgets in sidebar

Maybe I don’t know the right search criteria to find this answer, but I can’t believe it isn’t addressed more prominently. I need a widget area (sidebar) to contain common widgets for pages, then in that same widget area I need to have a location for adding a widget that will only appear on some pages. I COULD make multiple sidebars using a plugin, but I don’t want to have to update the common content across multiple sidebars every time. For instance, every page will have a sidebar nav menu, but some pages will have a lead generator on top of the menu. But to complicate it, there will be multiple lead generators that will appear on selected pages. Seems simple, right? Probably is but I’m stumped. Thanks for your help.