There is a product that 3M makes for preserving weatherstrips on cars, particularly for helping dry and damaged ones. If I'm not mistaken it is called "Krytox" - the main ingredient is Glycerin, I think. It is sort of expensive (around $30 a tube). It is available through Mid America Corvettes (a Corvette mail order outfit). I have used it on a few of my cars, and it does a very good job of "bringing back" damaged weatherstrips, as well as preserving new weatherstrips. If you have a frameless door, there might be a little smudging on the glass until it all sinks into the weatherstripping.