I'm another Gummi Pflege user. Got it originally for the various seals on my cabriolets, but I also use it on the GT86's seals.
It's especially useful in winter as it stops the window from freezing to the seal, with the risk of damage (either to the seal or to the window motor) when you open the door and the window tries to drop a little.
2013 GT86 - Burnt Orange
2015 Mazda MX-5 NC3 Sport Tech Nav Roadster Coupé - Jet Black
2008 Lexus IS 250 SE-L - Caspian Sky
2011 BMW E93 335i - Le Mans Blue