A friend gave me a Rolleicord Model III Type 2 to checkout. It belonged to her father and has been sitting for many years. It has the 75mm Zenar. The lens is very cloudy internally. I'm used to view camera lenses that just unscrew from the shutter for cleaning. On the Zenar the front has a knurled ring. Do you just use that ring to unscrew the front element group from the shutter? Maybe using the right size rubber stopper. The front also has a retaining ring but I'm assuming that it's used to remove the front lens to get between. Don't want to try to unscrew something that's not meant to turn.