Difficult to suggest what you might be able to use without knowing what products have been used on the window rubbers previously. Some dressing products with poor durability can sometimes leave similar marks on rubber when subjected to rain, car washing etc. improper use of a pressure washer (holding the lance too close and at right angles to the rubber) can produce a similar ‘staining’.
I’m assuming the staining is not the result of improper products being used on your car as I seem to recall you saying you’re a two bucket method car washer, so you’re unlikely to entrust car washing to one of the many hand wash car washing places, or use harsh washing products yourself.
You could try a solution of water and white vinegar to give the rubbers a thorough cleaning, and then use a good quality exterior rubber dressing product - one with good durability. However, it’s unlikely to be a permanent solution and there’s a chance that any such product would need to be reapplied periodically if the staining reappears or the rubbers take on a dull appearance.
It’d be worth doing a search on ‘restoring window rubber trims’ some of the detailing websites to see what might be an effective long lasting solution.