Re-viatalizing rubber hatch seals

I'm in the process of restoring my T114 and I carefully removed the rubber rear door hatch seal yesterday. it is in good shape but I want to do something to prevent it from drying out anymore. As said, it's in good shape (still pliable and soft) but one or two areas are starting to get a little less soft than others. What can I put on it to refurb it? thanks
Jason

I have put brake fluid on rubber seals with great results I was told by a old timer that it is a rubber conditioner.