Dupont KRYTOX GLP-205 is probably the best. Expensive, but a little goes a long ways.
They call it a Pure PFPE/PTFE grease, but a little rubbed on with a rag will protect the rubber from everything but 50 caliber armor piercing.
GM does not recommend Silicone, they recommend Krytox Oil (GM p/n 3634770), Ford's similar p/n is 164R4906 If I recall both are really DuPont Krytox GPL 105. I've used both the GM and DuPont products with great results dating back to my 2 door Cutlass Supreme days where the door glass seals and hard plastic guides would drive you nuts when they started squeaking. Krytox would cure it once and for good. Just used it to condition and get rid of squeaks on my F150 Panoramic Sunroof seals.
Some also have had good luck with nextzett 91480615 'Gummi Pflege Stift' but I stick with Krytox, not cheap but works.....
Edit-just saw Bruce's post above. The 100 series Krytox is a clear oil of varying viscosity, the 200 series is a white opaque paste, but same basic stuff