wsmm

Does anyone know if your can purchase the rubber diaphragm that goes under the cap on a Technovation clutch master cylinder. It appears to be made out of thin rubber and looks some what like a shot glass with a rim on it.. It there anything you can use in place of it? Would a flat piece of rubber or part of a plastic bag placed over the opening before placing on the cap work? Can you just leave it our, or will brake fluid come out of the mall vent hole in the cap when you depress and release the clutch? Can I just keep using the diaphragm that I have even though there are a few cracks (slits) in it? Plan on putting a new master cylinder in when the weather warms up a bit, this unit is on my plow truck.
Thanks,
Bill