the apex seals. One mistake some people made was to not rev them. They suck gas so many people thought it would use less if they drove it like grandma. Bad idea. Maintained properly and driven correctly they are very reliable. Pull up some YouTube or Wiki info in the 787b four rotor that won Le Mans. At the end of the 24 hours that motor was still in top condition and could have done another 24 hour race. Some say they only achieved a first and second place because the Mercedes cars blew up but isn't that a major component of an "endurance" race?!!! Also the sound that car made was unbelievable! Mazda made the best rotary, much better than NSU's versions. Emissions and consumption are poor but reliability is high.