No, you should not have to replace gaskets every time. Eventually they will get old and crack or get too soft and not seal tight, but that should take a long time. Most of the time when I get used kegs I replace the gaskets right away because they're cheap. Unfortunately poppets have gotten a *lot* more dear in the past few years.
Normally I put a little bit of cipfilm on the gaskets every time I clean one so the gaskets stay soft. It doesn't appear to dissolve or make the gaskets too soft.
There's a joke here about never having too much lube, but I'm not sure exactly where.
