Flush valve compatibility

[andrej82]

I just moved into a home with three Universal-Rundle toilets that seem to have worn-out flush valves. In previous houses, I would just get the exact manufacturer's valve at Home Depot or on PlumberSupplies.com and fix the problem in a minute. I've learned from experience, though, that "universal" valves are not universal at all and deviating from the exact maker results in more leaks than the old valve. However, I can't find a Universal-Rundle valve anywhere--only valve disks. Is there a chart or guide anywhere for valve compatibility? I don't want to buy 5 different "universal" or similar-looking brand-name valves, just to throw them out... (Or, if you know where to buy a Universal-Rundle valve, I'd great appreciate the info.)