I need to replace the bulb on the dials/wheels for the center and one side vent on a 1994 E320 coupe. Plenty of threads here advising how this is done.

My question is whether the vents need to be refitted snugly to ensure that, for example, when you have the heater on but don't want any cold air coming out of the centre vent this can be achieved through closing the vents and a tight fit. On my old 190E I resorted to fitting some cardboard cutouts behind the vents during winter because the setup was too loose and let cold air through.

Perhaps someone who's done this could explain whether this is something I have to worry about as I'd rather have no lit up dials as opposed to a leaky/whistly vent.