Yeah, I sort of agree with that - I have seen rubber patches and permatex used on cracked vacuum diaphragms and it does seem to work for a time. I used to think that it woulld affect the response time/amount of the slide, but I am told that apparently the vacuum creates a non-variable volume demand in the chamber controlling the slide and so material uniformity is less critical than it might be. The thing that kills diaphragms dead is being removed from the carb and left out in the open air, like on the workbench next to the window... if they haven't suffered ridiculous abuse you might be able to save them. By the by, sometimes slides and diaphragms are an assembled pair, and then things really get expensive, especially on a four. The Hondas with the machined vacuum chamber - which I guess this doesn't have - avoid this entire problem and have a system that lasts virtually forever, at the cost of slightly more real estate.
Umm, there are 2 per carb? You must mean the pullover-enrichener diaphragm on the side of the carb body? Those last pretty well unless they have had carb cleaner squirted in them, or been dipped in cleaner... they don't much care for that. Or do you mean maybe an accelerator pump?