You can repair pinhole light leaks in the bellows with either flat black textile paint or a mixture of Elmer's glue and lamp black. If using glue, leave the bellows open until it dries.
To test for leaks, I wired a lamp cord to a surface mount light socket and inserted a low wattage bulb. Turn out the lights, open the back of the camera, and place it
on top of the bulb. The pinholes will be obvious.