mercedes benz have a grease - its called something like glietpasten - blah. Its specifically used for slow moving high load parts plastic to plastic or plastic to metal parts like the sunroof sliders, window track sliders, power seat sliders and also in the wiper system - its waterproof and does not attract dust and is super slippery too.
I had a tin of it - 500 grams and cost me USD 86/- to buy - split the cost and grease too among a few. Worth every little penny. Its made by Dow Corning