I too had pin hole leaks in the bellows of my Deardorff. I solved the problem with neoprene cement. I live at the beach, close to surf and dive shops. It is a standard shelf item for the repair of wetsuits. Anyone living in less sublime environs can contact me for the brand name and you can research how to get some.
My biggest (literally) light leak problem was with my ancient Kodak Empire State 11x14 camera with a no-name back. This coupled with a weird array of holders, some with 80 year-old light traps. I solved this problem when my wife constructed a shower bonnet affair with black light-tight material which slips onto the back of the camera after the holder is inserted. A 12 in. slit on one side is protected with a 3 in. wide flap. This allows for removing and re-inserting the dark slide and covers the film holder during exposure. I had tried to do this with the focusing cloth, but it is very heavy and weighs down the back of the camera, affecting alignment. Also I defy anyone to stay under a dark cloth and remove a 15 in. long dark slide when the back is placed vertically. One would have to be 9 feet tall. The bonnet is compact and easily placed over the camera backs. No more light leaks.
PS Copyright is pending, and I made a bunch and will put them on e-bay. Bid to your hearts content. :-)