bit of an update for anyone that is interested.
I took the camera out on the back porch and had two shots loaded.
loaded the film holder in. replaced the normal wollensak mounted lensboard with a brand new completely undrilled blank lensboard so as too eliminate any light coming in from the front.
I pulled the darkslide and let the sheet of film "expose" to any light leaks for 20secs. I used 20 secs to over exagerate any light leaks to fully see their locations.
returned the darkslide and pulled out the film holder.
I then put my other film holder in and remounted my wollensak 12" lens. I covered up the entire camera with my focussing cloth. covered the bellows, the entire back standard and most of the front standard aside from the lens. I went under the focussing cloth and pulled the darkslide (all underneath the cloth) came out from underneath the focussing cloth. metered the scene and exposed the shot for 2 seconds per my light meter zone V reading.
took both film holders into the darkroom and developed them in my standard manner. PMK Pyro 1:2:100 at 800 seconds. Fixed and washed them.
Shot 1 (no lens mounted) showed horrible light leaks at the top of the film holder region. where the darkslide is removed and reinserted.
Shot 2 NO LIGHT LEAKS AT ALL. apparently covering everything up really made a huge difference.
So I went back outside and put a unloaded film holder in the camera and removed the front lensboard and got down under the dark cloth and look into the front of the camera.... after about 3 mins under there my eyes had adjusted and there were horrible light leaks coming in where the film holders sits against the back standard/spring loaded part.
Apparently there is no ridge for that part lengthwise notch on the film holders to rest on and the fabric that is working as a light seal isnt doing its job.
My plan is to take the back down to the fabric store and find some fabric that will work as a light sealer and strip the present fabric off and replace it with some 3m spray adhesive and the new fabric. I will likely also get out the dremel and cut a notch into the back to facilitate the notch "locking" that the film holders have.
any other suggestions anyone might have would be appreciated. and thanks again for the advice. the methodical testing seemes to help a great deal.
I am assuming that you mean the rib lock that camera backs have to allow the holder to be retained. If that is your problem then the remedy would appear to cut the necessary relief into your camera back.