Best stuff I've found for feeding rubber door seals and window felts is VW Special Lubricant Krytox Oil, part no. G052172A1. Get it from TPS (not via website) approx £38 for 30ml but a little goes a long way, and applied properly it has very long lasting effect. Imo, it's quite a lot better than gummi pflege, but either way, lubricating the seals which can dry out over time is one way to silence creaks/squeaks from seals.